Set Appliance State:
Mains Power Off
Set Multimeter to DC Volts 
Use Insulation Mat as required
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
With no demand the boiler may go into its pre-check sequence and ignite for up to 20 seconds, please wait for this to complete and for the appliance to go back to standby before taking any measurements.
Measure voltage across black wire (-ve probe) and the red wire (+ve probe) at connector J4 on the ignition pcb. Expected voltage 5 Volts DC.
Measure voltage across black wire (-ve probe) and the red wire (+ve probe) at connector J4 on the ignition pcb. Expected voltage 5 Volts DC.
Isolate as per TOPs P4
and refit as necessary