Set Appliance State:
Gas Off
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Ensure timer is in an ON period
Ensure timer is in an ON period
Measurement:
Disconnect the Main PCB Connector marked PL6 from the PCB.
Measure the resistance across the Brown and White wires on the CH Selector Switch.
Reconnect connector after test.
Measure the resistance across the Brown and White wires on the CH Selector Switch.
Reconnect connector after test.
Isolate as per TOPs P4
and refit as necessary