I had a new boiler and wireless thermostat (Honeywell) fitted in August. I've become increasingly convinced that the thermostat is set high. I have set the daytime temperature to go off at 20 degrees. When the heating comes on at 0630h (from a 14 degrees overnight setting so it's effectively off all night) the stat is still reading 19 after a coolish night. It rises to 21 and stays there for quite a while still calling for heat. It does eventually switch off the heat. Are these devices calibrated in a certain way as mine seems to love 21 degrees and is reluctant to let go? I also doubt that the temperature this morning is anything like 19 degrees in the hall, which feels cool to me.