Central heating comes on when thermostat in off position

[Mishasheba]

Hi
Had a new combi boiler (logic +) fitted last year to a tenants house. During the summer its been on summer mode but now when it is switched back to winter mode the central heating comes on straight away even if the hall wall thermostat is turned below the '0' setting. The radiators also start getting warm straight away and the thermostat does not seem to do anything. If I turn it up and down it does click on/off which I would have thought means its working OK but the rads just stay on all the time.

Any help appreciated here as it was only serviced a few weeks ago and the plumber said all was fine with it.

Regards

David

 

[ChrisOxford]

Was the thermostat installed at the same time as your new combi, or is it a remnant of your old system? If the latter, it's possible that the installer didn't connect it, or wired it in wrongly.

This kind of fault would not always necessarily be picked up on a routine service, I suspect.

 

[Mishasheba]

Hi, thanks for the reply. It was installed in March 2010 and was working fine up until she has tried to switch it back on after being in summer mode. The thermostat was therefore working fine up until she changed to summer mode only.

The service guy even tested it when he was there and showed me it going on/off on the unit but everytime she now switches it to winter mode the CH kicks in straight away. I thought there may be some sort of pre heat function but then there would be no reason for the rads to warm up with the stat off.

 

[Whitespirit66]

Which stat have you got?

 

[Mishasheba]

Hi, it's the same one that was there before on the old boiler, made by honeywell. Sorry can't expand anymore as there is no model number showing.

 

[Mishasheba]

Was the thermostat installed at the same time as your new combi, or is it a remnant of your old system? If the latter, it's possible that the installer didn't connect it, or wired it in wrongly.

This kind of fault would not always necessarily be picked up on a routine service, I suspect.

I have just taken the cover off the room stat to put a meter across the connections. The perm live is always live but when I cross from Neutral to switched live the meter needle drops down but does not go to the 'off' position. There seems to be permanent current there even after switching the mechanical dial on/off. Is this what's causing the CH to stay on and is it a boiler fault?

Having done the same on another stat in another house it goes from live to dead on the switched live when the stat is tuned up or down.

 

[D_Hailsham]

The perm live is always live but when I cross from Neutral to switched live the meter needle drops down but does not go to the 'off' position.

So at the stat there is 240Vac between Perm Live and Neutral?

What is the voltage between Switched Live and Neutral when the stat is turned to minimum?

What is it when the stat is turned to max?