Boiler won't turn off, heating on all the time

[HelenH]

I am hoping someone can help.  I am UK, not technical and will do my best to describe the problem.

We have 3rd gen Nest Thermostat

System Boiler (oil)

Water and Heating work independently

Everything has worked perfectly for a number of years with all this equipment.  However, in the last day or two the Nest just does not turn the boiler off.  Heating due to turn off at 10pm yesterday for instance, last night I woke in a sauna at 2am!  Nest thermostat showed the night temperature of 13.5 on a grey screen, however the boiler was kicking out more heat than it ever normally does.

What I have done...

I have factory reset the Nest thermostat

I have reset the Heat link

I have toggled the switch on the Sunvic motorised valve by our hotwater tank in case it has got stuck to on.

The only way I can stop the boiler firing up (despite the Nest showing it isn't heating) is to manually turn the boiler off.  If the boiler is turned on, it is heating 24 hours a day, despite what the Nest is saying.

For instance today... I manually turned the boiler on (I had to turn it off in the night because of the heat) and heating was due to go off at 0945hours.  That time came and went... boiler still firing up and heating.  Again I had to manually turn boiler off to stop the heating. Nest showing as 13.5 temperature with a grey screen. 

Could it be a problem with the Sunvic motorised valve not doing what it should do?

Sorry I can't be more technical with this, any help much appreciated. 

[MIchael51]

I have just started having exactly the same issue, but with combi boiler.  Heating due to switch off at 10pm last night, just kept going after thermostat said it had stopped.  Have tried re-set, doesn't work.  Am having to manually turn heating off and on.

[Michael_65]

Same problem here but with stored hot water (new boiler approx 1 year old) - manually switching off and on.  UK again.  3rd gen thermostat and 3rd gen heat link.

[TestDriver]

Hi, 

Have you found a solution to this problem? I've got the same issue you have with my Nest thermostat.

[HelenH]

Yes... it was not the Nest that was a problem.  It was the Motorised Zone Valve that turns the heating on and off.  It needed replacing.  The hot water one was fine, it was the heating one.  Bit fed up, as we had already replaced it a year ago, but it went again.