I’m assuming from the fact it’s on for a similar period of time and then of for a period of time, but is quite consistent within a few seconds, it’s a temperature issue.. or possibly flow
Only just found this site so first post here.
The boiler is an old vaillant combi that’s been here since we bought the house and to be honest other than a new fan and controller a few years back it’s never given us any issues.
The problem we have now is that the flame comes on for about 30...