Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
CH temperature selector to 0 position
DHW temperature selector to 0 position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Reset lockout as necessary.
Allow appliance to self check and return to standby mode.
DHW temperature selector to maximum position.
Does the fan run and burner ignite?