Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Measurement:
Remove the Grey and Brown wires (1) from the Gas Valve Solenoid Coil 1.
Measure the resistance across the two spade terminals on the Solenoid Coil.
The resistance measured should be approximately 900 ohms for SIT valve,
and 1500 ohms for Honeywell valve.
Reconnect wires after the test.
Measure the resistance across the two spade terminals on the Solenoid Coil.
The resistance measured should be approximately 900 ohms for SIT valve,
and 1500 ohms for Honeywell valve.
Reconnect wires after the test.
Isolate as per TOPs P4
and refit as necessary