RESET GAS VALVE

Isolate Mains Power to appliance as per TOPs P4
Reset Gas valve throttle settings by turning the gas valve "Throttle" screw fully clockwise then unscrew to approx 10 to 12 full turns anticlockwise

Observation:

WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure

Mains Power On
Apply a demand to the appliance.
Does burner now ignite and establish?

Note:
Upon successful diagnosis and repair you MUST reset the gas valve combustion settings as per Manufacturers commissioning procedure as set out in 12.6 of the manufacturers instructions.