boiler lights up runs for 4/5 seconds then cuts off on both h/w and heating replaced flame probe to no avail any ideas?

ricky d, July 2010

If the bolier lights but the electrodes keep sparking, and you have replaced the flame sensing probe, check the following:
A decent earth, Test from earth point on boiler to a known good earth supply
Polarity is correct between L&N
Readings should be
L to E ~240v
L to N ~240v
N to E 0-15 vac

If these are correct, visually inspect the flame sensing lead, otherwise it's pcb

Carefree, July 2010