Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
1. Attach a tube to the - port of the telegan and connect it to the top signal pressure test point on the gas valve
2. Attach another tube to the + port of the telegan and connect it to the bottom signal pressure test point on the gas valve
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.
Carry out a fan differential pressure test.
Does display show a differential pressure of at least 3 mb?
Note:
When the tubes are removed pressure test points should be tightened & checked for gas soundness.