Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove electrical connector from gas valve

Measurement:

Test 1. Measure for resistance across pins 1 & 4 of the gas valve terminals.
Expected resistance approximately 7.6 Kohms.
Test 2. Measure for resistance between pin 1 & a suitable earth connection.
Expected resistance 1 Mohm or greater.