Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect the connectors on the L/H side of the gas valve

Measurement:

Test 1:
Measure the resistance across the top pair of the four pins
on the L/H of the GV, expect approximately 80 Ohms.
Test 2:
Measure the resistance across the lower of the four pins
on the L/H of the GV, expect approximately 80 Ohms.
Test 3:
Measure the resistance from the top pin of the four pins
on the L/H of the GV a suitable either point.
Resistance should be greater than 1M Ohm.
Test 4:
Measure the resistance from the bottom of the four pins
on the L/H of the GV to a suitable either point.
Resistance should be greater than 1M Ohm.