Funny you say that!
I dont remembering telling you about my Christmas Response! Its the one you passed to me from Peter! Cost me 3-4 visits!
Stupid thing was blowing 3 A fuses every few days.
Got tenant to put in 13A fuse but that did not throw up anything either.
Eventually traced it to the LP switch which leaked internally just occasionally because the expansion vessel had failed.
Landlord job so replaced LP SW and configured a rad as exp vessel.
Tony