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Discuss Boiler fires up on HW demand but not on CH demand. in the Plumbing Forum | Plumbing Advice area at

Hi I have a fully pumped system. CH hasn't been used since April. Last Friday was a bit chilly so I turned the room stat up but the boiler didn't fire up. Boiler works when I demand HW. I installed a new room stat (Drayton RTS8) which made no difference. I then changed the controller from a Potterton EP2001 to an EP2 but that didn't solve the problem. I'm out of ideas. Can anyone suggest the next course of action please? Edit: Boiler is a Potterton Profile 40.
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Advent Win
Check that the HW control valve is opening when the CH is set to on and the thermostat set above ambient.

If it is not operating, and assuming that new controller and thermostat have been wired correctly, the problem is probably either the CH actuator or the CH valve.

Hope that helps

If the valve is operating, but the boiler does not fire, check the micro switch in the actuator.

If that does not identify the gremlin, check out the wiring continuity of the call for heat circuit from the controller to the boiler
Thanks Brambles. I haven't touched the wiring between the controller and boiler as the units have a common backplate so I just removed the old and plugged in the new. I have a 3-port valve on which, when calling for HW, the auto/manual lever is driven to the Auto position. If I then call for CH as well the lever is driven towards the manual position. If I then switch off the CH and demand HW the valve stays where it is until the lever is pushed all the way to the end of manual travel when the valve is then driven towards the auto position (possibly mid position). I think I'll have to get someone in to investigate further as I have a disability and haven't got sufficient dexterity to get into the boiler circuitry or valve actuator.

Thanks again for your time.


Please do not take this as a dig but as others read posts I always suggest my customers run their heating up to heat once a month during the off season so its for 15mins, electro mechanical equipment needs to be used in my opinion. centralheatking
Hi centralheatking
I never take good advice as a dig. I think the same about electro-mechanical kit but life happens and I forget. I do use the clocks changing as a reminder to exercise my stopcock and change my smoke alarm and CO2 detector batteries.
Update: I changed the three port valve to a Honeywell V4073A and everything works fine now. I looked at the Siemens 3P MPV 22 valve I removed and the cam operates one microswitch at the mid position. The cam just about moves the second microswitch at the open (CH) position but not enough to activate it. If I push the microswitch a little further with my finger I can hear the click.
Thanks for the advice.

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