Set Appliance State:
Set Multimeter to Resistance 
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Disconnect plug connector (marked ST16) from PCB
Disconnect plug connector (marked ST16) from PCB
Measurement:
Check resistance across connections 19 & 20 (pink wires). Resistance should be short circuit.
Note:
Care should be taken that probe tips do not touch each other when taking measurement as a false reading will be given. Also ensure that other end of the pink leads are connected to the diverter valve microswitch.
Note:
Care should be taken that probe tips do not touch each other when taking measurement as a false reading will be given. Also ensure that other end of the pink leads are connected to the diverter valve microswitch.
Isolate as per TOPs P4
and refit as necessary