Set Appliance State:
Gas Off
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Turn Hot Water Tap On
Measurement:
Remove the diverter valve microswitch cover and disconnect the microswitch multiplug.
Measure the resistance across the grey wire and pink wire on the 3 wire diverter valve microswitch.
Measure the resistance across the grey wire and pink wire on the 3 wire diverter valve microswitch.
Isolate as per TOPs P4
and refit as necessary