Set Appliance State:

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

Measurement:

Please be aware this model was produced after this gas valve became obsolete. This means we are not able to provide exact resistance readings, if a solenoid fails it will usually go open circuit (>1MΩ) or short circuit (zero resistance) so a readable resistance would generally indicate that the valve is ok.
Test 1:
Measure the resistance at the connections where the white and blue leads were previously connected.
Expect a readable resistance, considering the information given at the start of this test.
Measure the resistance where the white lead was connected to a suitable earth point.
Resistance should be greater than >1MΩ.
Test 2:
Measure the resistance at the connections where the black and blue leads were previously connected.
Expect a readable resistance, considering the information given at the start of this test.
Measure the resistance where the black lead was connected to a suitable earth point.
Resistance should be greater than >1MΩ.