In message , Paul G
writes

raden Wrote:
In message , Paul G
writes-

I have a problem with the above boiler in that the main burner will
not
light.
It seems that it is not flame sensing as the fan is rinning the pilot
lights but the spark gap (SG1) on the control board flashes in a
sequence that appears as if it is still trying to light the pilot.

The boiler's GC No. is: 4160166.

How does this boiler sense that the pilot has lit? Is it the electrode
that senses that the pilot is lit?
-
The pcb senses that the pilot light has lit electronically via the HT
lead

If it's not flame sensing
a) pcb is shagged (technical term)
b) HT lead is broken
c) electrode is not in the flame
d) bad earthing
e) dunno about the mercury switch

--
geoff

Thanks Geoff. The electrode and lead have both been changed and the
electdode is in the flame (I assume the resistance of the electrode
changes when hot then).
Where should I check for a bad earth? and I am not sure I have a
mercury switch, where would it be?

Earth from a good earth to where it goes to the pcb and where the
electrode housing is


this switch plugs into the gas valve IIRC

--
geoff