Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove Transformer from the PCB (This will require the removal of the metal back of the Control Box)

Measurement:

Check the resistance across both pairs of pins on the Transformer. Resistance of one pair of pins should be approximately 50 Ohms. Resistance on the other pair of pins should be approximately 1 Ohm.
Note: When testing, the pairing of the pins refers to the pins on the same side of the oblong shaped cavity in the base of the Transformer.