Set Appliance State:

On/Off Switch OFF
Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Disconnect gas valve electrical connector plug (held by one centre screw) from gas valve

Measurement:

Test 1.
Measure resistance across the two upper pins on the gas valve. Expected resistance approximately 1350 Ohms.
Test 2.
Measure resistance across the two lower pins on the gas valve. Expected resistance approximately 2900 Ohms.
Reconnect gas valve electrical connector plug after test.