Fan / pump OK, all voltages OK as per the fault-finding flowchart. Pilot lights but main burner will only light if gas valve sharply tapped with screwdriver / hammer. When the main burner cuts-off once operating temperature is reached- the gas valve needs a knock again to re-light main burner.
(Also- if the ceramic insulation is cracked on the ignition electrode- am I correct in assuming that the pilot wouldn't light? (to settle an argument))
(Also- if the ceramic insulation is cracked on the ignition electrode- am I correct in assuming that the pilot wouldn't light? (to settle an argument))