Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach U gauge to burner pressure test point
Remove the one lead from the modulating coil
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Measure the low gas pressure it should be approximately 2.0mb.
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.