Welcome to Google Nest.
monitor your home - does Google kerp it constant? Mine is maintained at 15C and won’t heat above it - even though it states heating to 18C. I’ve changed the calender, I’ve turned every setting off (except safety which is my last attempt today). I’ve recorded temperature, boiler, radiator status on an hourly basis (evidence - I see a class action on its way - or at least a call to watchdog). I even ran the system on manual over-ride for 24 hours. Whatever we do we can’t heat above 15C.
i Have however managed to heat our lounge to 16C by placing thermostat in utility room which has no heating!!!
i have spent 2 months dealing with Google support and had at least 3 calls of an hour trying things out. Plus Warmzilla who fitted the boiler - excellent after sales service. I have had British Gas out to check continuity of current (at Googles request). We have turned every radiator and the boiler to max.
googles end answer this week. They’ve sent a replacement nest & heatlink and advised that if this doesn’t work i should use an alternative supplier.
there are lots of complaints here from UK and US. The commonality I suspect is a software issue as I have two Google Nests both worked perfectly until I upgraded the software.