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CH stopped working, hot water fine.

Postby rforster » Sat Nov 17, 2007 1:29 am


I've come back from being a way a couple of days and the house is freezing, although plenty of hot water!

The system is open, gas fired Myson Orion boiler with Honeywell timer.

Before I went away, I had turned just the heating on on the timer, the boiler would fire.

This evening, when turning the heating on, the boiler didn't fire but would if H/W was turned on. With just CH on, I checked the thermostat and that was clicking at about 10 degree. That had no effect.

So, next I checked the control valve in the airing cupboard (Honeywell). The control valve has three connections - one from the pump, one to the hot water cylinder and one to elsewhere.

At first when I moved it to manual (open) from auto, nothing but I realised that when it was moved fully over to manual, rather than resting in the lock position, I could hear a microswitch and then I heard the boiler fire.

I'm sure that I've had this before.. Anyway. What should trigger the valve to move? Obviously when open, the switch is working but the valve closes - I've not had the top off but I'm guessing it is spring loaded?

So, I'm wondering what isn't working correctly. Is it the thermostat or is it the valve? How can I test that? I'm assuming that I should be able to take the thermostat out of the loop, ie bridge it somehow if I can work out the wiring.

I suppose if the valve then works, that points to the thermostat, else it is the valve?

For now, to get heating, if I put the valve into manual I can get the radiators to start to work. What I'm not sure of is if doing that, my radiators will only work when my hotwater needs heating - but having the valve in manual (open), does that mean I have CH and no H/W and with the valve the other way, H/W and no CH? For that, I can sort of live with whilst I sort the rest out.

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Simply Build It

Postby htg engineer » Sat Nov 17, 2007 9:07 pm

Sounds like you need to change the actuator, if you're competent you shouldn't find it too difficult. If your not confident then get a heating engineer to fit one for you.

It's really just a case of getting the correct actuator and wiring in the same as the old one.
htg engineer
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Postby rforster » Sun Nov 18, 2007 12:47 am


I sorted it thanks. I thought that it was probably the motor in the valve rather than the thermostat so just went and got one from the local suppliers first thing in the morning. Easy enough to fit.

Thanks for the response.

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