Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Turn Hot Water Tap On
Set flow rate to 2.8 litres a minute
Disconnect right hand plug from the PCB

Measurement:

Measure the resistance across the two pink
wires marked 23 and 24 at the disconnected plug.
Short circuit (zero resistance) expected.