I’m using a nest which doesn’t rise above 19C most days. Turned down the radiator heat on the boiler itself. 3 bed house. A few rads turned off and the main ones aren’t really turned up over 2/3.
I’ve received a huge bill, it’s particularly cold but This month my gas usage was 122kw/day, it was around 21kw/day last year according to bulb.
Did you have nest last year? If the heating is on all day I can see that been possible? It’s double my parents but they only have the heating on in the morning and evenings.
Worth noting that there’s an efficiency sweet spot for boilers. So turning down the heat on the boiler itself may not be helping things.