Set Appliance State:

Mains Power Off
CH Demand
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the fan run at high speed for approximately 10 seconds before stopping briefly (repeats 4 times before lockout). Or does the fan behave differently?

Note:
The fan can take up to 20 secs to start.