For both h/w and c/h the boiler will fire up for 3 seconds then stop for two seconds, fire up for 3 seconds then stop.. constantly. This appears to have occurred overnight. It is a Biasi Riva, five years old.
I replaced the h/w heat exchanger a year ago due to limescale, but even before then the c/h was fine and the problem was gradual.
Any ideas very welcome. Please post to group, I do not check that email address.
Many Thanks J