Set Appliance State:

Mains Power Off
Set Multimeter to DC Volts Set meter to measure DC Volts
NO Demands
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Test 1:
Measure the DC voltage between pin 1 (Blue) on connector X25 and a suitable earth.
Expect approximately 24 Vdc.
Test 2:
Measure the DC voltage between pin 2 (Red) on connector X25 and a suitable earth.
Expect approximately 24 Vdc.
Test 3:
Turn on the hot water tap.
When the boiler reaches the sparking stage of the ignition cycle measure the DC voltage between pin 1 (Blue) on connector X25 and a suitable earth.
Expect approximately 0 Vdc
Note:
Each pin on the PCB connector is numbered.