Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Attach pressure gauge to gas valve outlet pressure test point
Selector switch to DHW position
CH temperature selector to minimum
DHW Preheat selector to Off position
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow fan to run and burner to ignite and establish.
Is the burner pressure approximately 12.5 mb?
Isolate Mains Power to appliance as per TOP's P4
Disconnect one lead from the modureg and make safe.
Mains Power ON.
Allow fan to run and burner to ignite and establish.
Is the burner pressure approximately 1.8 mb?