Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
DHW Demand
Set FGA to Pressure setting
Disconnect the pressure tube from the gas valve and connect to it the positive pressure connection on the FGA
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Press reset to cancel purge cycle countdown.
As the fan runs during the ignition sequence is there a positive pressure of at least 1 mbar?