Set Appliance State:
Mains Power Off
Set Multimeter to DC Volts 
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
With a test probe on pin 1 of connector X7, monitor the DC voltage as the appliance goes through its self check
The voltage should fluctuate very briefly (approximately 7 seconds) before settling at approximately 22 Vdc.
Repeat the above test for pins 3, 4 and 6 (see note)
Do the voltages on pins 1, 3, 4 and 6 behave as described ?
Note.
When repeating the tests on pins 3, 4 and 6, it is important to mains power off then mains power on each time to avoid a misdiagnosis.
The voltage should fluctuate very briefly (approximately 7 seconds) before settling at approximately 22 Vdc.
Repeat the above test for pins 3, 4 and 6 (see note)
Do the voltages on pins 1, 3, 4 and 6 behave as described ?
Note.
When repeating the tests on pins 3, 4 and 6, it is important to mains power off then mains power on each time to avoid a misdiagnosis.
Isolate as per TOPs P4
and refit as necessary