Set Appliance State:

Mains Power Off
Ensure the plate heat exchanger is cool and the Pre Heat (Warm Start) is turned on
If the plate heat exchanger is already hot, isolate the electrical supply and run a hot tap until it runs cold
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Has the boiler fired to pre heat the plate heat exchanger?