Set Appliance State:
Gas Off
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Measurement:
Disconnect the Red wire (connection 2) and the Orange wire (connection 6) from the lighter switch button and measure the resistance across the switch.
Reconnect wires after test.
Note:
Lighter switch button is situated on the control panel, the control box will have to be opened to provide access to the leads. Care should be taken when reassembling the control box.
Reconnect wires after test.
Note:
Lighter switch button is situated on the control panel, the control box will have to be opened to provide access to the leads. Care should be taken when reassembling the control box.
Isolate as per TOPs P4
and refit as necessary