Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
Turn Hot Water Tap On
Gain access to PCB (use Insulation Mat as required)
Remove electrical connector from fan and make safe
Remove electrical connector from fan and make safe
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Reset appliance if required.
When the boiler has recognised a DHW demand (tap symbol flashing) measure the DC voltage between pin 4 (Yellow lead) on connector X20 and a suitable earth connection.
Expected voltage approximately 22 Vdc.
Note.
1. Pins are numbered on the connectors.
2. Appliance may enter lockout during test reset appliance as required until test complete.
When the boiler has recognised a DHW demand (tap symbol flashing) measure the DC voltage between pin 4 (Yellow lead) on connector X20 and a suitable earth connection.
Expected voltage approximately 22 Vdc.
Note.
1. Pins are numbered on the connectors.
2. Appliance may enter lockout during test reset appliance as required until test complete.
Isolate as per TOPs P4
and refit as necessary