Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove the left hand side panel of the appliance
Remove the electrical connector from the gas valve

Measurement:

Test 1:
Measure the resistance between the two outer pins on the gas valve 1 and 4.
Expect approximately 45 Ohms.
Test 2:
Measure the resistance between pin 4 on the
gas valve and the earth point on the boiler chassis.
Expected resistance greater than 1 MOhm.
Note:
Ensure a good connection is made or
misdiagnosis will occur.