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 lockout as necessary.
Allow appliance to self check and go to standby mode.
DHW temperature selector to maximum position.
Check for voltage at the terminal marked C (orange lead) at the air pressure switch and the neutral (blue lead) on connector J1 on the PCB.
Expected voltage approx 28 volts DC.
Allow appliance to self check and go to standby mode.
DHW temperature selector to maximum position.
Check for voltage at the terminal marked C (orange lead) at the air pressure switch and the neutral (blue lead) on connector J1 on the PCB.
Expected voltage approx 28 volts DC.
Isolate as per TOPs P4
and refit as necessary