Set Appliance State:
Gas Off
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove the diverter valve microswitch cover and disconnect the microswitch multiplug
Ensure the burner has been operating with a CH demand and the boiler has reached normal operating temperature
Ensure the burner has been operating with a CH demand and the boiler has reached normal operating temperature
Measurement:
Measure the resistance across the grey wire and the blue wire on the 3 terminal diverter valve microswitch.
Isolate as per TOPs P4
and refit as necessary