Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Open the control box by removing the two securing screws and lower the access door
Draw the control board forward to allow access to the PCB
Disconnect plug JP2 (1)
Remove the functional case door
Disconnect the flame detect lead from flame electrode (2)
Open the control box by removing the two securing screws and lower the access door
Draw the control board forward to allow access to the PCB
Disconnect plug JP2 (1)
Remove the functional case door
Disconnect the flame detect lead from flame electrode (2)
Measurement:
Measure the resistance of the flame detect lead (white wire).
Isolate as per TOPs P4
and refit as necessary