Set Appliance State:

Gas Off
CH Demand
Isolate Mains Power to appliance as per TOPs P4
Boiler Switch in ON position
Disconnect Pilot Supply from Pilot Block
Connect `U` gauge to Pilot Supply
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Check for presence of gas pressure at Pilot Supply.