My combi boiler was installed in May 2007 in the loft. Until recently (last six months or so) it has been trouble free but a fault has developed whereby at night time the boiler fires up and runs the heating for several minutes and then turns off. This then repeats throughout the small hours until morning. During the day it responds to the roomstat normally. Effectively, during the small hours it is overriding the temperature settings on the room stat. Last night I just had to turn the thing off and switch it back on this morning. I am thinking that this issue is related to colder temperatures in the loft space but what would cause the boiler to fire up and put the heating on overnight then behave itself during the day? My gas bill has increased dramatically this last quarter. What has changed in the last six months to cause it to do this? Glow worm 30Cxi.