Set Appliance State:

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

Measurement:

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