Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
System Pressurised
Remove wires (Yellow) from Water Pressure Switch

Measurement:

Measure short circuit resistance across the Water Pressure Switch (Yellow wires).
Note:
Some verisons of this appliance do not have a water pressure switch fitted.
If this is the case on your appliance select "Short circuit" from below.