Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Slacken the upper test point screw of the Gas Valve and attach a U-gauge
Selector switch to DHW position
CH temperature selector to minimum
DHW temperature selector to maximum
Both modureg wires connected
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow fan to run and ignition sequence to commence.
Does the burner ignite and go to full pressure of approximately 12.1 mbar?
Note: When U-gauge is removed the test point should be tightened and checked for gas soundness.