Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
DHW temperature selector to minimum setting so preheat does not operate
Ensure boiler is cool
Boiler On/Off switch On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset lockout if necessary.
Does the combustion fan start to run?