Set Appliance State:
Set Multimeter to DC Volts 
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
CH temperature selector to 0 position
DHW temperature selector to 0 position
CH temperature selector to 0 position
DHW temperature selector to 0 position
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Reset lock out as necessary.
Allow appliance to self check and go to standby mode.
DHW temperature selector to maximum position.
Allow fan to run and burner to ignite.
Check for voltage between connector J4 (grey lead) and the neutral (blue lead) on connector J1 on the main PCB.
Does the voltage remain constant?
Expected voltage approximately 28 volts DC.
Allow appliance to self check and go to standby mode.
DHW temperature selector to maximum position.
Allow fan to run and burner to ignite.
Check for voltage between connector J4 (grey lead) and the neutral (blue lead) on connector J1 on the main PCB.
Does the voltage remain constant?
Expected voltage approximately 28 volts DC.
Isolate as per TOPs P4
and refit as necessary