Set Appliance State:
Mains Power Off
Gas Off
Set Multimeter to DC Volts 
Turn Hot Water Tap On
DHW temperature set to maximum position
Flow rate at tap set to approx 7 ltr/min
Flow rate at tap set to approx 7 ltr/min
Gas On
Mains Power On
Measurement:
Allow boiler to run and heat DHW.
Measure voltage at the terminals of the modulating solenoid.
Does the voltage measured reduce as the temperature of the DHW increases?
Measure voltage at the terminals of the modulating solenoid.
Does the voltage measured reduce as the temperature of the DHW increases?
