Set Appliance State:

Mains Power Off
Gas Off
Set Multimeter to DC Volts Set meter to measure DC Volts
Central Heating Demand (selector switch in winter position)
Turn the adjustable Boiler Thermostat fully clockwise.
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure DC voltage across the connector on the Blue Solenoid.