Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove ignition PCB from gas valve and make safe

Measurement:

Test 1. Measure for resistance across pin 1 and pin 2 of exposed
gas valve connection.
Expected resistance approximately 1.7 Kohms.
Test 2. Measure for resistance across pin 4 and pin 5 of exposed
gas valve connection.
Expected resistance approximately 2.8 Kohms.
Test 3. Measure for resistance across each pin 1,2,4 and 5 of exposed
gas valve connections to pin 3 (green & yellow/earth) main terminal block.
Expected resistance open circuit.
Note.
Gas valve connection Pin 1 is nearest to the rear of the boiler