Baxi Boiler shutting down
 

I've got a problem with my Baxi WM51/3RS central heating boiler.
Everything seems to work fine but after around 5-10 minutes the boiler
stops burning and the whole system goes cold. Turning the controls
off and on after a couple of hours will cause it to burn again for
another 5 minutes, but it then shuts down again - otherwise the boiler
won't burn again. Pilot light stays lit.

From what I can tell, the pump, valve, themostat and controls all seem
to be working normally. When the boiler is actually firing, the
radiators will start to get hot and the pipe into the hot water tank
also gets hot, which suggests everything is ok.

My first guess was the boiler thermostat but replacing this hasn't
made any difference.

Second guess was a blockage or air lock causing the heated water not
to be leaving the boiler (thus triggering the stat), so I drained the
whole system (boiler included) and refilled it. Same problem.

Not sure how old the boiler is but I'm fairly sure its over 10 years
(as Baxi couldn't find it on their list and hence refused to send an
engineer out!). I'm beginning to accept I may just need to buy a new
boiler but don't want to do this and then discover the problem was
elsewhere!

System is a straight forward setup, conventional boiler, single
motorised valve, digital room thermostat and digital controls. Pump,
valve, thermostat and controls are all less than 2 years old and
everything was working fine up until this week.

Going to try bypass the room thermostat tonight and see if that makes
any difference (but I'm no electrician so may not have much success).

I'd be grateful for any ideas.

Cheers,
Steve

On Mon, 11 Oct 2004 08:20:58 -0700, steve wrote:

I've got a problem with my Baxi WM51/3RS central heating boiler.
Everything seems to work fine but after around 5-10 minutes the boiler
stops burning and the whole system goes cold. Turning the controls
off and on after a couple of hours will cause it to burn again for
another 5 minutes, but it then shuts down again - otherwise the boiler
won't burn again. Pilot light stays lit.

From what I can tell, the pump, valve, themostat and controls all seem
to be working normally. When the boiler is actually firing, the
radiators will start to get hot and the pipe into the hot water tank
also gets hot, which suggests everything is ok.

My first guess was the boiler thermostat but replacing this hasn't
made any difference.

Second guess was a blockage or air lock causing the heated water not
to be leaving the boiler (thus triggering the stat), so I drained the
whole system (boiler included) and refilled it. Same problem.

Not sure how old the boiler is but I'm fairly sure its over 10 years
(as Baxi couldn't find it on their list and hence refused to send an
engineer out!). I'm beginning to accept I may just need to buy a new
boiler but don't want to do this and then discover the problem was
elsewhere!

System is a straight forward setup, conventional boiler, single
motorised valve, digital room thermostat and digital controls. Pump,
valve, thermostat and controls are all less than 2 years old and
everything was working fine up until this week.

Going to try bypass the room thermostat tonight and see if that makes
any difference (but I'm no electrician so may not have much success).

I'd be grateful for any ideas.

Cheers,
Steve

Tell us why you think the pump is OK.
It might have a detached impellor if it is not just plain stuck.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

In an earlier contribution to this discussion,
steve wrote:

I've got a problem with my Baxi WM51/3RS central heating boiler.
Everything seems to work fine but after around 5-10 minutes the boiler
stops burning and the whole system goes cold. Turning the controls
off and on after a couple of hours will cause it to burn again for
another 5 minutes, but it then shuts down again - otherwise the boiler
won't burn again. Pilot light stays lit.

From what I can tell, the pump, valve, themostat and controls all seem
to be working normally. When the boiler is actually firing, the
radiators will start to get hot and the pipe into the hot water tank
also gets hot, which suggests everything is ok.

My first guess was the boiler thermostat but replacing this hasn't
made any difference.

Second guess was a blockage or air lock causing the heated water not
to be leaving the boiler (thus triggering the stat), so I drained the
whole system (boiler included) and refilled it. Same problem.

Not sure how old the boiler is but I'm fairly sure its over 10 years
(as Baxi couldn't find it on their list and hence refused to send an
engineer out!). I'm beginning to accept I may just need to buy a new
boiler but don't want to do this and then discover the problem was
elsewhere!

System is a straight forward setup, conventional boiler, single
motorised valve, digital room thermostat and digital controls. Pump,
valve, thermostat and controls are all less than 2 years old and
everything was working fine up until this week.

Going to try bypass the room thermostat tonight and see if that makes
any difference (but I'm no electrician so may not have much success).

I'd be grateful for any ideas.

Cheers,
Steve

It sounds as if you have an over-heat stat on the boiler which is tripping -
and that this can be reset by turning the temperature knob right down and up
again.

The most common reason for boilers overheating is insufficient water flow
due to a faulty pump or air lock. Are you *sure* your pump is running? Can
you remove the end cap and see the shaft going round? This would definitely
be my first port of call! [You might be getting *some* flow without the pump
running due to natural convection - causing the rads to start to warm up -
but not enough to stop the boiler from overheating.]
--
Cheers,
Set Square
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Set Square/Ed,

Thanks for your replies.

I've tried turning the temperature knob right down and up again but the
boiler still doesn't fire up.

As for the pump, I was assuming the pump was working because when the boiler
is running, all the radiators get hot (even the ones furthest away start to
get warm). However, I've now removed the bleed cap and I can see the shaft
moving round, though I guess it could still be a detached impellor. I could
turn the water flow off around the pump and take it apart to actually check
it's working correctly.

Not sure whether this is normal but when I first opened the bleed valve it
seemed like air was being sucked into the system. After a few seconds
though water started to drip out slowly.

Tonight I've ruled out the controls by bypassing the room thermostat and
hard wiring the main switch.

Also, when I first tried the boiler tonight I set the boiler stat to it's
lowest setting to try avoid it over-heating. It cut off after the usual 5
minutes or so. I then reset the controls and turned the stat up to max and
the boiler still didn't fire up. Also, you can hear the stat click and it's
not even as far as the first setting, which makes me think it's not actually
overheating - or the stat still isn't working - maybe I was sold a faulty
one?!

So if the pump is working what else could be causing the lack of flow?
Could it be a seriously corroded heat exchanger. I'm assuming there's no
air lock or blockage as I've done a full drain and the entire system is now
refilled - is that a safe assumption?.

If the flow is ok, could it be a faulty over-heat stat? Unfortunately I
don't have a manual for the boiler so can't find out how you'd go about
replacing it. I've checked Baxi's web site and they don't have manuals for
their older boilers. Would this even be a serviceable component?

Thanks again,
Steve


"Set Square" wrote in message
...
It sounds as if you have an over-heat stat on the boiler which is
tripping -
and that this can be reset by turning the temperature knob right down and
up
again.

The most common reason for boilers overheating is insufficient water flow
due to a faulty pump or air lock. Are you *sure* your pump is running? Can
you remove the end cap and see the shaft going round? This would
definitely
be my first port of call! [You might be getting *some* flow without the
pump
running due to natural convection - causing the rads to start to warm up -
but not enough to stop the boiler from overheating.]
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

In an earlier contribution to this discussion,
steve wrote:

Set Square/Ed,

Thanks for your replies.

I've tried turning the temperature knob right down and up again but
the boiler still doesn't fire up.

As for the pump, I was assuming the pump was working because when the
boiler is running, all the radiators get hot (even the ones furthest
away start to get warm). However, I've now removed the bleed cap and
I can see the shaft moving round, though I guess it could still be a
detached impellor. I could turn the water flow off around the pump
and take it apart to actually check it's working correctly.

Not sure whether this is normal but when I first opened the bleed
valve it seemed like air was being sucked into the system. After a
few seconds though water started to drip out slowly.

Tonight I've ruled out the controls by bypassing the room thermostat
and hard wiring the main switch.

Also, when I first tried the boiler tonight I set the boiler stat to
it's lowest setting to try avoid it over-heating. It cut off after
the usual 5 minutes or so. I then reset the controls and turned the
stat up to max and the boiler still didn't fire up. Also, you can
hear the stat click and it's not even as far as the first setting,
which makes me think it's not actually overheating - or the stat
still isn't working - maybe I was sold a faulty one?!

So if the pump is working what else could be causing the lack of flow?
Could it be a seriously corroded heat exchanger. I'm assuming
there's no air lock or blockage as I've done a full drain and the
entire system is now refilled - is that a safe assumption?.

If the flow is ok, could it be a faulty over-heat stat? Unfortunately
I don't have a manual for the boiler so can't find out how you'd go
about replacing it. I've checked Baxi's web site and they don't have
manuals for their older boilers. Would this even be a serviceable
component?

Thanks again,
Steve


What sort of control valve does your system have. Is it a 3-port
mid-position valve to direct the water from the boiler either to the HW
circuit or the CH circuit or both together? Is there also a
thermostat on the hot water cylinder? What is that set at?

When the boiler fails to fire, is the pump still running? What do you
actually have to do to get the boiler to fire again? [You mentioned turning
the controls off and on. *Which* controls?]
Does the boiler have a reset button which has to be pressed in to make it
work again?
--
Cheers,
Set Square
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is it a powered flue model?

steve

--
To reply to me direct, remove the SPACE's from my email address!
"steve" wrote in message
om...
I've got a problem with my Baxi WM51/3RS central heating boiler.
Everything seems to work fine but after around 5-10 minutes the boiler
stops burning and the whole system goes cold. Turning the controls
off and on after a couple of hours will cause it to burn again for
another 5 minutes, but it then shuts down again - otherwise the boiler
won't burn again. Pilot light stays lit.

From what I can tell, the pump, valve, themostat and controls all seem
to be working normally. When the boiler is actually firing, the
radiators will start to get hot and the pipe into the hot water tank
also gets hot, which suggests everything is ok.

My first guess was the boiler thermostat but replacing this hasn't
made any difference.

Second guess was a blockage or air lock causing the heated water not
to be leaving the boiler (thus triggering the stat), so I drained the
whole system (boiler included) and refilled it. Same problem.

Not sure how old the boiler is but I'm fairly sure its over 10 years
(as Baxi couldn't find it on their list and hence refused to send an
engineer out!). I'm beginning to accept I may just need to buy a new
boiler but don't want to do this and then discover the problem was
elsewhere!

System is a straight forward setup, conventional boiler, single
motorised valve, digital room thermostat and digital controls. Pump,
valve, thermostat and controls are all less than 2 years old and
everything was working fine up until this week.

Going to try bypass the room thermostat tonight and see if that makes
any difference (but I'm no electrician so may not have much success).

I'd be grateful for any ideas.

Cheers,
Steve

Set Square,

Yes, it's a 3-port mid-position valve.

I'm not sure about the hot water cylinder thermostat. There's a wire
that runs to a plastic housing which is fixed to the bottom of the
cylinder but I've not taken it apart and can't find any setting
switch. I'll try taking that apart tonight and see if there's some way
I can bypass it.

Yes, when the boiler shuts down, the pump continues to run.

The boiler will only fire again after waiting for about an hour and
then switching the controls off and back on. By 'controls' I mean the
Timer switch that controls when the ch/hw comes on (this is seperate
to the boiler - a Lifestyle LP522). By switching I mean setting both
the hw and ch switches to 'off' and then back to 'on'. There's no
reset button on the boiler that needs pressing, just a recycle of the
controls.

From what I can tell the boiler won't fire unless the controls are
recycled but I'd have to sit and watch it for a couple of hours to be
100% sure - looks like I'm in for thrilling evening!

Cheers,
Steve

"Set Square" wrote in message ...

What sort of control valve does your system have. Is it a 3-port
mid-position valve to direct the water from the boiler either to the HW
circuit or the CH circuit or both together? Is there also a
thermostat on the hot water cylinder? What is that set at?

When the boiler fails to fire, is the pump still running? What do you
actually have to do to get the boiler to fire again? [You mentioned turning
the controls off and on. *Which* controls?]
Does the boiler have a reset button which has to be pressed in to make it
work again?

In an earlier contribution to this discussion,
steve wrote:

Set Square,

Yes, it's a 3-port mid-position valve.

I'm not sure about the hot water cylinder thermostat. There's a wire
that runs to a plastic housing which is fixed to the bottom of the
cylinder but I've not taken it apart and can't find any setting
switch. I'll try taking that apart tonight and see if there's some way
I can bypass it.

Yes, when the boiler shuts down, the pump continues to run.

The boiler will only fire again after waiting for about an hour and
then switching the controls off and back on. By 'controls' I mean the
Timer switch that controls when the ch/hw comes on (this is seperate
to the boiler - a Lifestyle LP522). By switching I mean setting both
the hw and ch switches to 'off' and then back to 'on'. There's no
reset button on the boiler that needs pressing, just a recycle of the
controls.

From what I can tell the boiler won't fire unless the controls are
recycled but I'd have to sit and watch it for a couple of hours to be
100% sure - looks like I'm in for thrilling evening!

Cheers,
Steve


Ok, we've got to try to isolate this problem a bit! Can you get at the
boiler wiring? The boiler should have a switched live connection - which
comes from the progammer, stats, mid-position valve etc. to tell it when to
fire. When it fails to fire at the right time, is this connection live? If
it *is*, it indicates a problem within the boiler. If it *isn't*, it
indicates a problem in the external controls - for which the actuator on the
mid-position valve would be my prime suspect.

What happens if you cycle the controls *without* waiting for an hour?
--
Cheers,
Set Square
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Set Square,

I got to the main wiring terminal and that just connects another wire which
runs to the gas valve. I checked at both points and there's definitely a
live connection when the boiler should be firing.

This also confirms what I tried last night which was to bypass the room stat
and timer.

I guess it doesn't rule out any internal wiring within the gas valve unit
though? I could replace this but I've never suspected the gas valve as the
boiler is capable of firing up.

Just cycling the controls whenever the boiler has shut down has no affect
other than it switching the pump on and off respectively. Also, in all the
time I've spent messing around I've never seen the boiler come on without a
cycle of the controls.

I tried a few things to get the boiler to fire and your original suggestion
of turning the boiler thermostat down and up seemed to have some effect.
After I'd waited for everything to cool down, the usual cycle of the
controls caused the boiler to fire up. I immediately turned the controls
off and the boiler correctly shut down. I then turned the controls back on
but the boiler didn't fire. When I turned the stat down and back up and
cycled the controls the boiler fired again (albeit only for about 2
seconds). I've tried to repeat this though without any success, but I'll
keep trying.

Does this imply a dodgy over-heat stat or are we back to the original idea
of it being a circulation problem?

If it's the over-heat stat, where is this likely to be located and is it
serviceable?

The pipe from the boiler is getting hot when the boiler runs which implies
there is flow from the boiler but maybe it's not sufficient like you
suggested. As I said in the original post though, when the boiler does run
for its longest time, all the radiators start to get hot implying there
isn't any blockage.

Once again I'd be really grateful if you could offer anymore good ideas.

Cheers,
Steve.


Ok, we've got to try to isolate this problem a bit! Can you get at the
boiler wiring? The boiler should have a switched live connection - which
comes from the progammer, stats, mid-position valve etc. to tell it when
to
fire. When it fails to fire at the right time, is this connection live? If
it *is*, it indicates a problem within the boiler. If it *isn't*, it
indicates a problem in the external controls - for which the actuator on
the
mid-position valve would be my prime suspect.

What happens if you cycle the controls *without* waiting for an hour?
--
Cheers,
Set Square
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On Tue, 12 Oct 2004 21:51:07 +0100, steve wrote:

I tried a few things to get the boiler to fire and your original suggestion
of turning the boiler thermostat down and up seemed to have some effect.
After I'd waited for everything to cool down, the usual cycle of the
controls caused the boiler to fire up. I immediately turned the controls
off and the boiler correctly shut down. I then turned the controls back on
but the boiler didn't fire. When I turned the stat down and back up and
cycled the controls the boiler fired again (albeit only for about 2
seconds). I've tried to repeat this though without any success, but I'll
keep trying.

Does this imply a dodgy over-heat stat or are we back to the original idea
of it being a circulation problem?


Looks like we have some sort of boiler problem.

I'm not at all familiar with this model however it would be very helpful
to know its general design.
a) Very low tech, permanent pilot light no electronics, possibly a 230V-24V
transformer for the gas valve. Over-heat sensor (if present) will simply be
in series with the thermocouple. Boiler does not have a permanent live
supply.

b) Electronics present: over heat done by a seperate sensor requiring
a power down and up to reset. Might or might not have a permanent pilot.

Sounds like type 'a' can't give you the problems whilst type 'b' could.
In which case the over heat sensor (or its wiring?) is too enthusiastic.
Does the boiler have any warning lights?

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

In an earlier contribution to this discussion,
steve wrote:

Set Square,

I got to the main wiring terminal and that just connects another wire
which runs to the gas valve. I checked at both points and there's
definitely a live connection when the boiler should be firing.

This also confirms what I tried last night which was to bypass the
room stat and timer.

I guess it doesn't rule out any internal wiring within the gas valve
unit though? I could replace this but I've never suspected the gas
valve as the boiler is capable of firing up.

Just cycling the controls whenever the boiler has shut down has no
affect other than it switching the pump on and off respectively.
Also, in all the time I've spent messing around I've never seen the
boiler come on without a cycle of the controls.

I tried a few things to get the boiler to fire and your original
suggestion of turning the boiler thermostat down and up seemed to
have some effect. After I'd waited for everything to cool down, the
usual cycle of the controls caused the boiler to fire up. I
immediately turned the controls off and the boiler correctly shut
down. I then turned the controls back on but the boiler didn't fire.
When I turned the stat down and back up and cycled the controls the
boiler fired again (albeit only for about 2 seconds). I've tried to
repeat this though without any success, but I'll keep trying.

Does this imply a dodgy over-heat stat or are we back to the original
idea of it being a circulation problem?

If it's the over-heat stat, where is this likely to be located and is
it serviceable?

The pipe from the boiler is getting hot when the boiler runs which
implies there is flow from the boiler but maybe it's not sufficient
like you suggested. As I said in the original post though, when the
boiler does run for its longest time, all the radiators start to get
hot implying there isn't any blockage.

Once again I'd be really grateful if you could offer anymore good
ideas.

Cheers,
Steve.


Bit of a problem, this one!

Like you, I can't find any reference to this model on Baxi's website in
order to be able to download a manual.

My Baxi Solo boiler (which is now about 10 years old) has a diagnostic chart
printed on the back of the part of the casing which has to be unclipped to
get at the controls. Does yours have anything like that?

From the symptoms which you now describe, it is beginning to sound like a
problem with the main gas valve - probably its solenoid. If the pilot light
is on, and the gas valve is is being told to open but fails to do so, it
suggests something in that area. Does your boiler have a PCB? If so, that
could just be faulty - possibly with a dry joint somewhere. It seems
possible that when everything is cold it works ok, but as soon as it warms
up (and I'm talking here of the electrics warming up rather than the water
system - but they go hand in hand) either something loses contact on the
PCB - if there is one - or the solenoid no longer has sufficient urge to be
able to keep the gas valve open. When everything cools down again, it's ok.
This doesn't really explain the effect of turning the controls off and on
again - but that could be resetting something.

Hopefully someone who remembers that boiler (Geoff?) will come forward with
some ideas based on knowledge rather than conjecture!
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

steve used his keyboard to write :
As for the pump, I was assuming the pump was working because when the boiler
is running, all the radiators get hot (even the ones furthest away start to
get warm). However, I've now removed the bleed cap and I can see the shaft
moving round, though I guess it could still be a detached impellor. I could
turn the water flow off around the pump and take it apart to actually check
it's working correctly.

As you close the valves near the pump with it running, you should hear
the change in the noise. It would saving you actually removing the pump
to check the impellor.

--


--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.org

Ed,

It's definitely in the 'a' category. Permanent pilot, no electronics,
no controls other than the stat and the pilot ignitor. All the wiring
and controls are seperate - junction box in the airing cupboard
linking the valve, hot water cylinder stat etc... and a seperate
timer/programmer control unit.

Coming into the boiler is just one live supply which is then directly
and only linked to another wire going into the gas valve unit. Boiler
themostat is a seperate box which seems to be wired directly into the
gas valve unit (and obviously the sensor going into the heat
exchanger).

There's nothing else of note in the boiler, no PCB or warning lights.
Seems everything is contained within the gas valve unit.

Cheers,
Steve

"Ed Sirett" wrote in message on.co.uk...

Looks like we have some sort of boiler problem.

I'm not at all familiar with this model however it would be very helpful
to know its general design.
a) Very low tech, permanent pilot light no electronics, possibly a 230V-24V
transformer for the gas valve. Over-heat sensor (if present) will simply be
in series with the thermocouple. Boiler does not have a permanent live
supply.

b) Electronics present: over heat done by a seperate sensor requiring
a power down and up to reset. Might or might not have a permanent pilot.

Sounds like type 'a' can't give you the problems whilst type 'b' could.
In which case the over heat sensor (or its wiring?) is too enthusiastic.
Does the boiler have any warning lights?

Set Square,

There is a diagnostic chart on the back of the casing but it's not
particularly useful. There's no symptom that describes my problem and
the closest (pilot on but boiler not firing) suggests it's either the
boiler thermostat, closed governor (?), external controls or... doh,
can't remember - in work at the moment - I'll post back tonight if
there's anything else on there.

I could replace the gas valve unit and rule that out - found a place
(http://www.mjtcontrols.co.uk) selling the unit for £30+VAT which is
siginficantly cheaper than a new boiler! The unit is pretty much the
main part of the boiler so there's a good chance it would solve the
problem, assuming it's not a problem with the water flow.

Cheers,
Steve


"Set Square" wrote in message ...
Bit of a problem, this one!

Like you, I can't find any reference to this model on Baxi's website in
order to be able to download a manual.

My Baxi Solo boiler (which is now about 10 years old) has a diagnostic chart
printed on the back of the part of the casing which has to be unclipped to
get at the controls. Does yours have anything like that?

From the symptoms which you now describe, it is beginning to sound like a
problem with the main gas valve - probably its solenoid. If the pilot light
is on, and the gas valve is is being told to open but fails to do so, it
suggests something in that area. Does your boiler have a PCB? If so, that
could just be faulty - possibly with a dry joint somewhere. It seems
possible that when everything is cold it works ok, but as soon as it warms
up (and I'm talking here of the electrics warming up rather than the water
system - but they go hand in hand) either something loses contact on the
PCB - if there is one - or the solenoid no longer has sufficient urge to be
able to keep the gas valve open. When everything cools down again, it's ok.
This doesn't really explain the effect of turning the controls off and on
again - but that could be resetting something.

Hopefully someone who remembers that boiler (Geoff?) will come forward with
some ideas based on knowledge rather than conjecture!

On 13 Oct 2004 01:16:49 -0700, (steve) wrote:

Set Square,

There is a diagnostic chart on the back of the casing but it's not
particularly useful. There's no symptom that describes my problem and
the closest (pilot on but boiler not firing) suggests it's either the
boiler thermostat, closed governor (?), external controls or... doh,
can't remember - in work at the moment - I'll post back tonight if
there's anything else on there.

I could replace the gas valve unit and rule that out - found a place
(http://www.mjtcontrols.co.uk) selling the unit for £30+VAT which is
siginficantly cheaper than a new boiler! The unit is pretty much the
main part of the boiler so there's a good chance it would solve the
problem, assuming it's not a problem with the water flow.

Hi,

Try finding the overheat thermostat and temporarily bypass it to see
if it runs longer, - but switch off if the water in the boiler starts
kettling! You'll need to find out if it's normally open or closed and
bypass it accordingly.

If it still cuts out then the problem is elsewhere, possibly another
sensor or loose connection.

cheers,
Pete.

In an earlier contribution to this discussion,
steve wrote:

Set Square,

There is a diagnostic chart on the back of the casing but it's not
particularly useful. There's no symptom that describes my problem and
the closest (pilot on but boiler not firing) suggests it's either the
boiler thermostat, closed governor (?), external controls or... doh,
can't remember - in work at the moment - I'll post back tonight if
there's anything else on there.

I could replace the gas valve unit and rule that out - found a place
(http://www.mjtcontrols.co.uk) selling the unit for £30+VAT which is
siginficantly cheaper than a new boiler! The unit is pretty much the
main part of the boiler so there's a good chance it would solve the
problem, assuming it's not a problem with the water flow.

Cheers,
Steve


It sounds from your other post in response to Ed's that the boiler is pretty
basic - with no fancy electronics. It should thus be easy to diagnose -
because there are very few things to go wrong.

I'm pretty sure now that you *don't* have an over-heat stat - and that lack
of flow won't make it trip - so the problem has to be within the boiler
itself.

It only has a few components which - I believe - work as follows: [I am sure
that you - or others - will correct me if there are any glaring errors in
this description/analysis]

The gas valve control is actually 2 separate valves to control both the
pilot light and the main burner. In order to light the pilot light, you have
to hold in a button on the gas valve to over-ride the flame protection
device, and press another button to generate a spark. Once the pilot lights,
it heats up a thermocouple which causes the pilot valve to remain open -
enabling the over-ride button to be released.

The boiler thermostat is an electrical switch which opens and closes
depending on whether the boiler output water temperature is above or below
the set temperature. The required temperature is set by turning a knob, and
the actual temperature is measured by a bulb, on the end of a capillary
tube, which is inserted into a housing on the heat exchanger. [This contains
a liquid whose pressure varies with temperature, and the electrical switch
is actually operated by a pressure capsule - and turning the knob biases the
operating point].

The main gas valve is operated by a mains-voltage solenoid which is
energised when fed by mains current- coming from the programmer/room stat
etc. and wired via the boiler thermostat. It has an interlock which prevents
it from firing unless the pilot is lit - as detected by the thermocouple.
_____

If the above is correct, and if the boiler fails to fire when fed with a
demand signal, one or more of the following must be happening:
* The boiler thermostat could be faulty. [This could be eliminated by
temporarily bypassing it]
* The solenoid could be faulty [Seems the most likely to me - works for a
bit and then its windings get warm and go high resistance or open circuit.
Works again when it cools down]
* The interlock is faulty [Seems unlikely, since the pilot stays on ok]

If it fires when the stat is bypassed, but not otherwise, replace the stat.
If bypassing the stat doesn't do the trick, I think I'd take a flier and
replace the gas valve.

--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

In message , Set Square
writes
In an earlier contribution to this discussion,
steve wrote:

Set Square,

I got to the main wiring terminal and that just connects another wire
which runs to the gas valve. I checked at both points and there's
definitely a live connection when the boiler should be firing.

This also confirms what I tried last night which was to bypass the
room stat and timer.

I guess it doesn't rule out any internal wiring within the gas valve
unit though? I could replace this but I've never suspected the gas
valve as the boiler is capable of firing up.

Just cycling the controls whenever the boiler has shut down has no
affect other than it switching the pump on and off respectively.
Also, in all the time I've spent messing around I've never seen the
boiler come on without a cycle of the controls.

I tried a few things to get the boiler to fire and your original
suggestion of turning the boiler thermostat down and up seemed to
have some effect. After I'd waited for everything to cool down, the
usual cycle of the controls caused the boiler to fire up. I
immediately turned the controls off and the boiler correctly shut
down. I then turned the controls back on but the boiler didn't fire.
When I turned the stat down and back up and cycled the controls the
boiler fired again (albeit only for about 2 seconds). I've tried to
repeat this though without any success, but I'll keep trying.

Does this imply a dodgy over-heat stat or are we back to the original
idea of it being a circulation problem?

If it's the over-heat stat, where is this likely to be located and is
it serviceable?

The pipe from the boiler is getting hot when the boiler runs which
implies there is flow from the boiler but maybe it's not sufficient
like you suggested. As I said in the original post though, when the
boiler does run for its longest time, all the radiators start to get
hot implying there isn't any blockage.

Once again I'd be really grateful if you could offer anymore good
ideas.

Cheers,
Steve.


Bit of a problem, this one!

Like you, I can't find any reference to this model on Baxi's website in
order to be able to download a manual.

My Baxi Solo boiler (which is now about 10 years old) has a diagnostic chart
printed on the back of the part of the casing which has to be unclipped to
get at the controls. Does yours have anything like that?

From the symptoms which you now describe, it is beginning to sound like a
problem with the main gas valve - probably its solenoid. If the pilot light
is on, and the gas valve is is being told to open but fails to do so, it
suggests something in that area. Does your boiler have a PCB? If so, that
could just be faulty - possibly with a dry joint somewhere. It seems
possible that when everything is cold it works ok, but as soon as it warms
up (and I'm talking here of the electrics warming up rather than the water
system - but they go hand in hand) either something loses contact on the
PCB - if there is one - or the solenoid no longer has sufficient urge to be
able to keep the gas valve open. When everything cools down again, it's ok.
This doesn't really explain the effect of turning the controls off and on
again - but that could be resetting something.

Hopefully someone who remembers that boiler (Geoff?) will come forward with
some ideas based on knowledge rather than conjecture!

Hmm, p pilot, no pcb

no experience, no idea.

The obvious possibilities have already been mentioned

--
geoff

In an earlier contribution to this discussion,
Pete C wrote:


Hi,

Try finding the overheat thermostat and temporarily bypass it to see
if it runs longer, - but switch off if the water in the boiler starts
kettling! You'll need to find out if it's normally open or closed and
bypass it accordingly.

If it still cuts out then the problem is elsewhere, possibly another
sensor or loose connection.

cheers,
Pete.

I'm pretty sure it hasn't got one - older boilers didn't. [See my post of
8.14pm]

--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

On 13 Oct 2004 01:16:49 -0700, (steve) wrote:

Set Square,

There is a diagnostic chart on the back of the casing but it's not
particularly useful. There's no symptom that describes my problem and
the closest (pilot on but boiler not firing) suggests it's either the
boiler thermostat, closed governor (?), external controls or... doh,
can't remember - in work at the moment - I'll post back tonight if
there's anything else on there.

I could replace the gas valve unit and rule that out - found a place
(http://www.mjtcontrols.co.uk) selling the unit for £30+VAT which is
siginficantly cheaper than a new boiler! The unit is pretty much the
main part of the boiler so there's a good chance it would solve the
problem, assuming it's not a problem with the water flow.

Hi,

Another thing, check there is enough water in it. Sometimes if there's
not enough the level can drop slightly while the boiler runs and make
it cut out.

cheers,
Pete.

On Wed, 13 Oct 2004 00:50:41 -0700, steve wrote:

Ed,

It's definitely in the 'a' category. Permanent pilot, no electronics,
no controls other than the stat and the pilot ignitor. All the wiring
and controls are seperate - junction box in the airing cupboard
linking the valve, hot water cylinder stat etc... and a seperate
timer/programmer control unit.

Coming into the boiler is just one live supply which is then directly
and only linked to another wire going into the gas valve unit. Boiler
themostat is a seperate box which seems to be wired directly into the
gas valve unit (and obviously the sensor going into the heat
exchanger).

There's nothing else of note in the boiler, no PCB or warning lights.
Seems everything is contained within the gas valve unit.


Have you put a probe/multi-meter or neon tester on the gas valve?
This will split the problem between the gas valve or the thermostat.
My gut feeling is that it will be the thermostat because you find that you
need to turn it down and up to get a result.

The themrostat is like less than £20.
If you replace the gas valve make sure you know what you are doing.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

We have a winner!

Replaced the gas valve this evening and so far everything is working
normally again!

Sincere thanks to everyone that contributed ideas, particulary Set Square.

Steve



"Set Square" wrote in message
...
In an earlier contribution to this discussion,
It sounds from your other post in response to Ed's that the boiler is
pretty
basic - with no fancy electronics. It should thus be easy to diagnose -
because there are very few things to go wrong.

I'm pretty sure now that you *don't* have an over-heat stat - and that
lack
of flow won't make it trip - so the problem has to be within the boiler
itself.

It only has a few components which - I believe - work as follows: [I am
sure
that you - or others - will correct me if there are any glaring errors in
this description/analysis]

The gas valve control is actually 2 separate valves to control both the
pilot light and the main burner. In order to light the pilot light, you
have
to hold in a button on the gas valve to over-ride the flame protection
device, and press another button to generate a spark. Once the pilot
lights,
it heats up a thermocouple which causes the pilot valve to remain open -
enabling the over-ride button to be released.

The boiler thermostat is an electrical switch which opens and closes
depending on whether the boiler output water temperature is above or below
the set temperature. The required temperature is set by turning a knob,
and
the actual temperature is measured by a bulb, on the end of a capillary
tube, which is inserted into a housing on the heat exchanger. [This
contains
a liquid whose pressure varies with temperature, and the electrical switch
is actually operated by a pressure capsule - and turning the knob biases
the
operating point].

The main gas valve is operated by a mains-voltage solenoid which is
energised when fed by mains current- coming from the programmer/room stat
etc. and wired via the boiler thermostat. It has an interlock which
prevents
it from firing unless the pilot is lit - as detected by the thermocouple.
_____

If the above is correct, and if the boiler fails to fire when fed with a
demand signal, one or more of the following must be happening:
* The boiler thermostat could be faulty. [This could be eliminated by
temporarily bypassing it]
* The solenoid could be faulty [Seems the most likely to me - works for a
bit and then its windings get warm and go high resistance or open circuit.
Works again when it cools down]
* The interlock is faulty [Seems unlikely, since the pilot stays on ok]

If it fires when the stat is bypassed, but not otherwise, replace the
stat.
If bypassing the stat doesn't do the trick, I think I'd take a flier and
replace the gas valve.

--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

In an earlier contribution to this discussion,
steve wrote:

We have a winner!

Replaced the gas valve this evening and so far everything is working
normally again!

Sincere thanks to everyone that contributed ideas, particulary Set
Square.

Steve


Excellent!

Since, in order to fit the new valve, you had to remake the gas connections,
I trust that you did a leak test when it it was back together?

If not, do it now! You can get an aerosol of foamy stuff from a plumbers
merchant which you spray onto all gas connections. If there's even the
slightest leak, you'll see bubbles.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

Since, in order to fit the new valve, you had to remake the gas
connections,
I trust that you did a leak test when it it was back together?

If not, do it now! You can get an aerosol of foamy stuff from a plumbers
merchant which you spray onto all gas connections. If there's even the
slightest leak, you'll see bubbles.

Is there anything wrong with watered down washing up liquid and a brush?

Bob

In an earlier contribution to this discussion,
Bob Smith (UK) wrote:

Since, in order to fit the new valve, you had to remake the gas
connections, I trust that you did a leak test when it it was back
together?

If not, do it now! You can get an aerosol of foamy stuff from a
plumbers merchant which you spray onto all gas connections. If
there's even the slightest leak, you'll see bubbles.

Is there anything wrong with watered down washing up liquid and a
brush?

Bob

I don't know! Earlier this year we had our gas main - and the pipe into the
house - renewed, as part of Transco's gas main renewal programme. When it
was all done, they sent in a gas fitter to make sure that everything worked.
He disconnected the boiler to bleed the feed pipe, and then checked the
joint once he had re-connected it. To do this, he had some liquid in one of
the sort of plastic cannisters we might use for spraying the roses! He swore
blind that this was some special substance approved by BG/Transco - and that
anything else might prove to be corrosive.

I'm still nor sure whether he was "for real" - or whether it was actually
Fairy Liquid!
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Bob Smith (UK) wrote:

Since, in order to fit the new valve, you had to remake the gas
connections, I trust that you did a leak test when it it was back
together?

If not, do it now! You can get an aerosol of foamy stuff from a
plumbers merchant which you spray onto all gas connections. If
there's even the slightest leak, you'll see bubbles.

Is there anything wrong with watered down washing up liquid and a
brush?

Bob

I don't know! Earlier this year we had our gas main - and the pipe into
the
house - renewed, as part of Transco's gas main renewal programme. When it
was all done, they sent in a gas fitter to make sure that everything
worked.
He disconnected the boiler to bleed the feed pipe, and then checked the
joint once he had re-connected it. To do this, he had some liquid in one
of
the sort of plastic cannisters we might use for spraying the roses! He
swore
blind that this was some special substance approved by BG/Transco - and
that
anything else might prove to be corrosive.

I'm still nor sure whether he was "for real" - or whether it was actually
Fairy Liquid!

Detergent is supposed to be loaded with chlorides which do corrode whereas
the "approved" liquids aren't and don't

"John" wrote in message
...

"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Bob Smith (UK) wrote:

Since, in order to fit the new valve, you had to remake the gas
connections, I trust that you did a leak test when it it was back
together?

If not, do it now! You can get an aerosol of foamy stuff from a
plumbers merchant which you spray onto all gas connections. If
there's even the slightest leak, you'll see bubbles.

Is there anything wrong with watered down washing up liquid and a
brush?

Bob

I don't know! Earlier this year we had our gas main - and the pipe into
the
house - renewed, as part of Transco's gas main renewal programme. When
it
was all done, they sent in a gas fitter to make sure that everything
worked.
He disconnected the boiler to bleed the feed pipe, and then checked the
joint once he had re-connected it. To do this, he had some liquid in one
of
the sort of plastic cannisters we might use for spraying the roses! He
swore
blind that this was some special substance approved by BG/Transco - and
that
anything else might prove to be corrosive.

I'm still nor sure whether he was "for real" - or whether it was
actually
Fairy Liquid!

Detergent is supposed to be loaded with chlorides which do corrode whereas
the "approved" liquids aren't and don't



Could wipe it down afterwards I suppose.

Bob

I don't know! Earlier this year we had our gas main - and the pipe into
the
house - renewed, as part of Transco's gas main renewal programme. When
it
was all done, they sent in a gas fitter to make sure that everything
worked.
He disconnected the boiler to bleed the feed pipe, and then checked the
joint once he had re-connected it. To do this, he had some liquid in one
of
the sort of plastic cannisters we might use for spraying the roses! He
swore
blind that this was some special substance approved by BG/Transco - and
that
anything else might prove to be corrosive.

I'm still nor sure whether he was "for real" - or whether it was
actually
Fairy Liquid!

Detergent is supposed to be loaded with chlorides which do corrode whereas
the "approved" liquids aren't and don't



No-one seems to mind having flux dribbling down the insides of gas pipes...

Bob

"Bob Smith (UK)" wrote in message
...

I don't know! Earlier this year we had our gas main - and the pipe
into
the
house - renewed, as part of Transco's gas main renewal programme. When
it
was all done, they sent in a gas fitter to make sure that everything
worked.
He disconnected the boiler to bleed the feed pipe, and then checked
the
joint once he had re-connected it. To do this, he had some liquid in
one
of
the sort of plastic cannisters we might use for spraying the roses! He
swore
blind that this was some special substance approved by BG/Transco -
and
that
anything else might prove to be corrosive.

I'm still nor sure whether he was "for real" - or whether it was
actually
Fairy Liquid!

Detergent is supposed to be loaded with chlorides which do corrode
whereas
the "approved" liquids aren't and don't



No-one seems to mind having flux dribbling down the insides of gas
pipes...


Well actually they do but don't let me spoil your idea.

I WOULD JUST LIKE TO SAY THANKS FOR THE INFORMATION I GOT ABOUT THE
BAXI WM51/3RS CENTRAL HEATING BOILER.
ALTHOUGH I HAVE NEVER HAD A PROBLEM WITH THIS EXCELLENT :D BOILER
(WHICH WAS INSTALLED IN 1986) IT IS NOW GETTING ON A BIT, AND THE
INFO. I GOT FROM DIYPROJECTS.INFO WILL BE HELPFUL AND IS VERY MUCH
APPRECIATED.
SO MANY THANKS TO ALL.
DAVID MORTON

In message , mighty 1
writes
I WOULD JUST LIKE TO SAY THANKS FOR THE INFORMATION I GOT ABOUT THE
BAXI WM51/3RS CENTRAL HEATING BOILER.
ALTHOUGH I HAVE NEVER HAD A PROBLEM WITH THIS EXCELLENT :D BOILER
(WHICH WAS INSTALLED IN 1986) IT IS NOW GETTING ON A BIT, AND THE
INFO. I GOT FROM DIYPROJECTS.INFO WILL BE HELPFUL AND IS VERY MUCH
APPRECIATED.

So the muppets who read diyprojects can't even find the caps lock key
-LHS near the bottom sunshine

Tosser


The information contained in this post
may not be published in, or used by
http://www.diyprojects.info


--
geoff