Set Appliance State:
Mains Power Off
Set Multimeter to DC Volts 
Turn Hot Water Tap On
Selector switch to DHW position
CH temperature selector to minimum
DHW Preheat selector to OFF position
CH temperature selector to minimum
DHW Preheat selector to OFF position
Gas On
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Allow fan to run and burner to ignite.
Measure the voltage across the modulating solenoid terminals. Approximately 8-10 volts should be present.
Measure the voltage across the modulating solenoid terminals. Approximately 8-10 volts should be present.
Isolate as per TOPs P4
and refit as necessary