Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Remove brown and blue leads from bottom gas valve solenoid

Measurement:

There are two types of gas valve and solenoid that may be fitted to the appliance.
Measure resistance between the exposed terminals of the bottom solenoid.
Type A: Resistance should be approximately 1.5k Ohms.
Type B: Resistance should be approximately 600 Ohms.