Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
DHW Demand
Connect temperature clamps to heat exchanger flow and return pipes.
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Press reset to cancel purge cycle countdown.
Allow burner to fire for DHW and flow temperature to reach 55°C.
Measure the temperature differential of the flow and return.
Expected differential should be 20°C or less.