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 temperature selector to maximum
CH temperature selector to minimum
DHW temperature selector to maximum
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Allow fan to run and burner to ignite.
Measure the DC voltage across the modulating
solenoid terminals.
Approximately 8-10 Volts DC should be present.
Measure the DC voltage across the modulating
solenoid terminals.
Approximately 8-10 Volts DC should be present.
Isolate as per TOPs P4
and refit as necessary