hi was wondering if anyone can help me with a problem im having with a riello rdb burner on a warflow condensing boiler i looked at today.it runs fine for anything from 10 mins to 20 mins then loses pressure from 9bar to zero.it then either relights or cycles on and off a bit but doesnt lockout.coil and photocell are fine and oil pump filter is totally clean.convential flue so its not choking on its own fumes so any help wiould be much appreciated.runs great for a while but wont keep it up.