Nest gone mad

[m0t]

I've got a Nest thermostat which is nearly 7 years old an I believe is a version 2. We had a lot of issues with it in the early years but for the past few it's worked happily away in the background.

I had my latest gas bill a few weeks back and it was much higher than expected, more similar to a bill from January. It's not been warm but not as cold as that.

We noticed at the weekend some odd behaviour from the Nest. It's showing the target temperature (in this case 22), the actual temperature (22) and it then turned the heating on and got it up to 23, all whilst showing the correct target temp of 22. I've reset it but it's still doing it.

Is there anything I can do to fix it or does it need replacing?

 

[ericmark]

I have found with Nest gen 3 that it has things like anti-legionnaires which can be switched off, and auto learning which can be switched off, even much cheaper thermostats had anti-hysteresis software, what this does is start a make/space ratio as the target temperature is approached switching the boiler off for longer and longer as it gets closer to the target, this worked well with non modulating boilers, but with modulating boilers it stopped the boiler from modulating, not sure on gen 2 if it had this option, wants turning off with a modulating boiler.

However if a thermostat turns on the boiler when already warm enough, it should not really cost that much, as the TRV sets room temperature so as soon as the water has circulated it should turn boiler off again and you will end up with boiler turning on at lowest output one an hour for around 2 minutes, i.e. long enough for the water to circulate through the by-pass valve, so seems likely there is some thing else wrong as well.