I have a 10 year old Alpha 240p Boiler which is causing me a mare at the moment. With HW tap open burner lights up but cuts out after 20 secs then relights again 10 seconds later resulting in hot cold showers. This same issue is occurring with the CH the rads are only getting warm as the burner keeps shutting off after 20 secs then relighting. Any help would be much appreciated.