Set Appliance State:

Mains Power Off
Function selector in Standby position
Hot tap ON
Selector Switch to Hot Water and Heating
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Turn function selector to DHW position.
Allow fan to run and ignition sequence to complete approximately 4 seconds after burner has ignited.
Can the fan speed be heard to increase?