Set Appliance State:

Mains Power Off
Gas On; Pilot On
Turn Hot Water Tap On
Selector Switch in HW position.
HW Thermostat to Max.
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Run Hot Water for approximately two minutes.
Is there a 35 degree C rise at a flow rate of 9L/min?