Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove flame sense electrode from heat exchanger
Measurement:
Thoroughly check the electrode and lead for signs of damage, cracked ceramic insulation, cleanliness and good general condition.
Measure the resistance across the electrode.
Expect continuity / zero resistance.
Refit electrode after test.
Also check the probe has not distorted away from the burner, if in doubt measure the gap between the burner and the electrode as shown. The gap should be 22mm +/-1mm.
Measure the resistance across the electrode.
Expect continuity / zero resistance.
Refit electrode after test.
Also check the probe has not distorted away from the burner, if in doubt measure the gap between the burner and the electrode as shown. The gap should be 22mm +/-1mm.
Isolate as per TOPs P4
and refit as necessary