Google Nest calling for heat when Thermostat off (new issue, working fine before)

[Jordan_L]

Hi all,

Our Gen 3 Nest Thermostat has been working fine for about 1.5 years. System boiler, with Nest Thermostat wired into previous location of the old thermostat (so wired for power, not battery powered)

Tonight, I noticed that the CH was running despite there being no call for CH or HW. Three-port valve is about 6 months old, was set in CH position.

I tried setting the Nest to call for CH, call for HW, both off etc and still it continued to run.

In the end I had to turn power off to the heating system from the fuse board. 

Why would this happen all of a sudden, was working absolutely fine yesterday.  Are there known issues?

Thanks,

Jordan

[zoeuvre]

Hi Jordan_L, 

Yikes! I'm sorry to hear that your thermostat is calling for heat even though it's off. Are you located in North America or Europe? What type of Nest Thermostat do you have? You may follow the steps here in the troubleshoot strange heating or cooling behavior article for a fix.

Let us know how it goes.

Best,

Zoe