Central Heating controls question: Boiler not responding

[shannyla]

Our heating system has stopped responding to calls for heat from the thermostat. Thermostat is a Siemens wireless, relay opening and closing due to demands from the thermostat checked with meter and appears to be working correctly. Programmer is a Honeywell ST9400C, wiring is standard Honeywell Wiring Center. Single pump, system splits through two Honeywell 2-port valves, one for Ch, one for HW. CH valve can be opened by hand and if left open, radiators are hot when boiler is producing heat when called for by HW stat.

Boiler responds correctly to calls for heat from hot water tank thermostat. My question is, does this sound like failure of the CH valve motor? I'm assuming that the boiler won't fire until the programmer knows that the valve has actuated.

Thanks for any help.

 

[picasso]

Does the ch valve open on demand but the boiler does not fire ? if the valve opens then the micro switch isint making, if it isint opening then check you have 240v on the brown wire, if you do then the motor is shot.

 

[shannyla]

I don't think the valve is even trying to open, I certainly can't hear it, whereas the HW valve is noisy enough to hear if you listen closely. Is the microswitch inside the valve, and does it need to make to allow the programmer to fire the boiler?

That would certainly explain the lack of boiler response. My initial thoughts were that the relay in the thermostat receiver had gone but my testing ruled that out.