Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
CH temperature control to max
Connect FGA to the combustion test point on the boiler
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Adjust gas valve (CO/CO2 ratio) to the manufacturers specified values, refer to Adapt for guidance / procedure.