Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
Turn Hot Water Tap On
Set DHW flow rate at tap to approximately 5 l/min and allow
DHW to run cold
Remove lower facia panel
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow boiler to ignite.
Monitor the voltage across the terminals of the modulating solenoid (blue wires).
Does the voltage reduce as the DHW temperature demand is met?
Note:
Plug shown for clarity.