Central Heating Not Responding To Control Properly

[GregHH]

Would appreciate some help with a CH control mystery please. My boiler has stopped responding to the room thermostat/control properly. The boiler only fires when it is receiving a call from the hot water side. If I turn the hot water off at the controller then the boiler goes off regardless of the CH controller and thermostat setting. While the hot water is calling for heat the boiler stays on and the radiators heat up.
I've tested the thermostat and it seems to be fine. When the controller has CH on, mains power is getting to the thermostat and is correctly switched on/off by the knob. The problem seems to be that that signal is not getting to the boiler. I assume that the problem must be somewhere around the valves/pump but I'm not familiar with how they are likely to be wired up. Any suggestions?

 

[75pete]

I'm not a heating engineer but I would say it points towards the mid position diverter valve not working as should. Anyway that's my first thought.
Next...

 

[GregHH]

Thanks Pete. I've had a look and I have two Honeywell V4032 zone valves. Would the CH valve seizing open give my symptoms do you think?

 

[45yearsagasman]

If it was stuck open then the rads would heat up when the hot water is on. Chances are that the synchron motor in the ch valve has failed. Remove the top cover and check for 230v at the motor and check motor for continuity.
Obviously you need a meter and work safely.

 

[75pete]

A new motor head can be got from people like screwfix etc. If the valve needs to be removed and a new one fitted, some can be changed without the need to drain the system. Do a Search for more info. i think the cover needs to have a "bump" in it, this shows that you can remove the unit with out the need to drain. Do check im correct before going ahead.
pete

 

[GregHH]

Manual auto lever on the valve is moving with little or no resistance so I know where the problem is now. Thanks