Set Appliance State:

Mains Power Off
Set Multimeter to DC Volts Set meter to measure DC Volts
CH Demand
CH temperature control to maximum
DHW temperature control to minimum
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow the burner to ignite and, after approximately 3 to 4 seconds,
measure the voltage across the connections of the modulating solenoid.
The actual voltage measured will depend on the range rating of the boiler.
The boiler comes factory set to its mid range which should give approx. 10Vdc at the solenoid.
(Max voltage on CH is approx.16Vdc (35.4mb for Propane, 27.2mb for Butane) and Min approx. 1Vdc (6.1mb for Propane, 4.7mb for Butane)
Is the voltage measured between 1 and 16Vdc?