Set Appliance State:
Gas Off
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Measurement:
Disconnect the two White wires (that connect the transformer to the PCB) from the PCB noting their positions and measure the resistance across them.
The resistance should be approximately 4 ohms.
Note1: Resistance above includes fused multimeter lead resistance of 3 ohms.
Note2: Transformer is situated inside the control box, the control box will have to be opened to provide access to the leads. Care should be taken when opening and reassembling control box.
Reconnect wires after test.
The resistance should be approximately 4 ohms.
Note1: Resistance above includes fused multimeter lead resistance of 3 ohms.
Note2: Transformer is situated inside the control box, the control box will have to be opened to provide access to the leads. Care should be taken when opening and reassembling control box.
Reconnect wires after test.
Isolate as per TOPs P4
and refit as necessary