Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Attach a U-gauge to the burner pressure test point
Programmer or selector switch set to hot water only
Hot water temperature selector to maximum
Heating temperature selector to OFF
Ensure heatbank is not up to temperature (this can be achieved by running the DHW with the mains power to the appliance on and the gas to the appliance turned off)
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Does the U-gauge show pressure remaining above 18mb throughout the ignition sequence?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.