Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove both ends of the flame sense harness, from the electrode and from the top of the ignition PCB
Measurement:
Measure the resistance of the flame sense harness lead.
Inspect the flame sense electrode for good overall condition.
Inspect the flame sense electrode for good overall condition.
Isolate as per TOPs P4
and refit as necessary