Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Identify the heating zone valve electrical lead and terminal connections used

Measurement:

Measure the resistance between the brown wire of the heating zone valve and the main neutral.
Expect 2 - 3Kohms.
Note: The colour and position of the wires will vary between systems and components.