Set Appliance State:

CH Demand
Isolate Mains Power to appliance as per TOPs P4
Turn on HW tap allow water to flow to dissipate heat in secondary heat exchanger
Disconnect one of the violet wires on the Pre-heat thermostat and make safe
Turn off HW tap
CH/HW switch to CH position
ON/OFF switch ON
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Does secondary heat exchanger get hot?