boiler switching on when not programmed

[daverunt]

My boiler is switching on when not programmed. The program lights are alos off at the time. I suspect the programmer but could it be anything else?

[buildersmate]

Some systems have a frost-stat fitted which over-rides absolutely every other programmer/setting. This is to fire up the boiler when it gets very chilly to prevent freezing of pipes and such stats are more likely to have been fitted if the boiler is mounted in an outhouse or garage.
Its not very cold just now, but if you've got such a stat, could it be malfunctioning?

[kwicky]

My frost stat turns on my boiler when the temperature goes below 5 degrees centigrade.