Set Appliance State:

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

Measurement:

Test 1:
Measure the resistance between pins 1 and 3 on the gas valve.
 
Expect approximately 26 Ohms.
Test 2:
Measure the resistance between pins 2 and 4 on the gas valve.
 
Expect approximately 68 Ohms.
Test 3:
Measure the resistance between pin 1 on
the gas valve to a suitable earth point.
 
Resistance should be greater than 1M Ohm (or O.L.)
Test 4:
Measure the resistance between pin 2 on
the gas valve to a suitable earth point.
 
Resistance should be greater than 1M Ohm (or O.L.)