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
______
Please reply to newsgroup. Reply address is invalid.

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
______
Please reply to newsgroup. Reply address is invalid.

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
______
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

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

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 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 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


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--
geoff