Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect the inline connector to the safety fuse harness from the main boiler harness
Remove connector from safety fuse (located top left of primary heat exchanger)
Remove connector from safety fuse (located top left of primary heat exchanger)
Measurement:
Measure the resistance of each of the wires in the safety fuse harness.
Expect continuity on each wire.
Expect continuity on each wire.
 connector safety fuse harness.gif)
 inner,covers,removed,resize.gif)
Isolate as per TOPs P4
and refit as necessary