Set Appliance State:

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

Measurement:

Measure the resistance between the pins on the gas valve.
Resistances should be approximately as in the table below.
PinsResistance
1 - 36.7 kOhms
3 - 4 880 ohms

Note:
The pins on the gas valve should be numbered.