I had a new boiler installed in May so only just started using it to heat the house. I hate it. When it's cold and I want to override the manual schedule I turn up the thermostat from say 17 to 20 and it says it will reach temp in +2 hrs. Why? My old thermostat would kick in instantly and take about 10 mins to reach temp??
The nest learning thermostat is exactly doing that, it is learning. When the system Heat gets turned on and the heat starts, the system learns how long it took to go from say 17 to 20°C. Over time, it will learn the amount of time to reach the temperature will become more and more accurate. So for now, don’t worry about how long it says, and pay attention to how long it does.
The AC Cooling Wizard