not sure why central heating systems always breakdown in winter and at the
start of the week...but hey..

My problem is that the boiler comes on, there is hot water in the tank but
the radiators are cold. Pump is working fine. If i twiddle the living-room
thermostat the burner fires up for about 10 secs and then turns off.

If i manually lock open the 3-way valve then then the radiators get hot, but
otherwise the 3-way valve stays closed.

I'm thinking that the living room thermostat has gone?? If so, it is simply
a case of swapping it out?
Or could it be the PCB that has a problem??

cheers
martin

Tell us wther the Hot Water is on the "A" or "B" side of the 3 way
valve.
It could be that yout tank thermostat has welded itself clsoed, thus
demanding Hot Water all the time, and over riding the central heating
demand.

If i manually lock open the 3-way valve then then the radiators get hot,
but
otherwise the 3-way valve stays closed.

The most likely culprit is the 3 port valve, although Y-plan wiring can have
some odd failure modes with failed contacts or damaged wiring.

Christian.

"Martin" wrote in message
...
not sure why central heating systems always breakdown in winter and at the
start of the week...but hey..

My problem is that the boiler comes on, there is hot water in the tank but
the radiators are cold. Pump is working fine. If i twiddle the living-room
thermostat the burner fires up for about 10 secs and then turns off.

If i manually lock open the 3-way valve then then the radiators get hot,
but
otherwise the 3-way valve stays closed.

I'm thinking that the living room thermostat has gone?? If so, it is
simply
a case of swapping it out?
Or could it be the PCB that has a problem??


start with the simple things. Is there power to the motor in the valve?
Valve motors are the commonest failure

In message , Martin
writes
not sure why central heating systems always breakdown in winter and at the
start of the week...but hey..

My problem is that the boiler comes on, there is hot water in the tank but
the radiators are cold. Pump is working fine. If i twiddle the living-room
thermostat the burner fires up for about 10 secs and then turns off.

If i manually lock open the 3-way valve then then the radiators get hot, but
otherwise the 3-way valve stays closed.

It sounds like either the synchron motor has gone on the 3 port valve or
(and since you didn't say what the boiler is, it's impossible to say,
but lets assume that it's driven from the pcb) the PCB isn't driving the
valve
--
geoff