Central Heating Sometimes Won't Turn Off

[Seekayem]

Hi

Have a problem with my central heating; it doesn’t always turn off when thermostat reaches set temp and clicks off. The pump and boiler keep going; radiators remain hot. Usually have to turn thermostat back up to full, leave a minute or so then lower and often this does the trick. It will then likely behave itself for a while (radiators coming on and off with the thermostat as normal) but eventually it will do it again.

This has been happening for the last 2 weeks but for the last year there has been a similar problem, although this time the pump and boiler (intermittently) continued but the radiators did actually cool down when the thermostat reached the set temp. I lived with this since the radiators were being heated and cooling down in line with the thermostat setting;

The system has a Drayton z5 Zone Valve Actuator. I noticed that sometimes when the problem occurred I could get the heating to shut off if I played with the manual lever at the top. I wondered whether the actuator motor was on the way out so I replaced it with a new Synchronous Motor yesterday but the problem persists.

Should I try a whole new Zone Valve Actuator? Or could the problem be elsewhere?

The boiler is an Ideal Classic FF260. Tank is a Megflo.

Hope someone can help. Thanks

Chris

 

[seco services]

Sounds like the valve is jamming in the open position activating the micro switch so it keeps the boiler pump running.
Look on the side of the valve it will have a marker A B if the marker is on B
when stat is satisfied and boiler keeps running the valve is jammed open.

The marker should return to the A position when heating off or satisfied.

You can remove the actuator from the brass valve and see if it returns properly on it's own to position A if it does the spindle in the brass valve is more likely stiff and full of crud not allowing the spring to pull it back.

You can operate the spindle with a pair of pilers see if it moves freely.

 

[Seekayem]

Thanks for that very quick response.

I think it was stuck in the B position when it last acted up. At the moment it is behaving itself i.e. if I adjust the thermostat it correctly turns itself on and off so I need to wait for it to go wrong again before I can be certain what position it is stuck in.

I have taken it off the spindle though and the spindle does turn using my fingers.

Will report back when problem re-surfaces.

Also, and this will be my stupidest question so far, but the heating works when the actuator is (temporarily) removed from the valve completely. So what is the valve actually doing? I assumed everything (boiler etc) was being turned on/off electronically.

 

[seco services]

Also, and this will be my stupidest question so far, but the heating works when the actuator is (temporarily) removed from the valve completely. So what is the valve actually doing? I assumed everything (boiler etc) was being turned on/off electronically.

The top part the actuator is all the elecs so will still operate the boiler/pump
if your holding it in your hand. It still turns inside to operate the m/switch.
The brass part is just a paddle that the valve opens so the water can flow through the valve.