Exactly what are you setting for 12 degrees constant? Hot water? Room temperature? Something else?
As far as I can see from the manual, there's no way to set room temperature on the boiler:
https://www.freeboilermanuals.com/assets/pdf/British-Gas/532-537-42-LPG.pdf
Is it the room thermostat you are trying to set as a frost precaution, maybe? If so, make and model of that.
Vhhjj, January 2023
