Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Attach U gauge to burner test point
Selector Switch in DHW Summer position
Hot Water Thermostat set to Maximum
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Is burner pressure greater than 1.9 mbar, ideally at 12.3?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.