Set Appliance State:

Mains Power Off
CH Demand
Locate and identify the heating zone valve.
Ensure the room thermostat is turned to its max position.
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Inspect the Indicator lever on the side of the valve, at rest with no demand the lever should be in the A position.
Once a demand is placed the valve should open moving the lever to the B position.
Does the valve operate as described?