Heating will not switch off

[devonboy]

CH has been operating fine until today, but now the heating will not switch off when room temperature reached, does the thermostat need replacing?

Thanks for any assistance.

 

[kevin clayton]

CH has been operating fine until today, but now the heating will not switch off when room temperature reached, does the thermostat need replacing?

Thanks for any assistance.

I had this problem with underfloor heating. I could only turn it off using the timer. It turned out that it was an electrical part hidden out of view. This had to be replaced. Suggest you try switching the timer and see if it goes off. If it does it is not your thermostat.

 

[devonboy]

Timer calls for heat, thermostat calls for heat, boiler comes on, when temperature reached heat does not switch off.
Checked the stat with a meter between L & N is 240v, between yellow switch wire and N is 240v which goes to zero when temperature reached, therefore the problem does not appear to be the thermostat, could it be the 3 way valve?
Only way to shut down heating is to set the timer to off.

 

[imjohnbrown86]

Setting timer off can help, try that.

 

[devonboy]

Don't know if this helps but been playing around with different settings of timer and thermostat.
Timer calls for heat and hot water plus thermostat on - result radiators and water warm up.
Thermostat reaches desired temperature and clicks off but the radiators get hotter.
Switch heating off from timer radiators continue to get hotter.
Switch hot water off from timer, radiators cooldown.
Therefore tried switching the hot water off completly from timer then radiator system works fine switching on and off via the thermostat.