Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
DHW Demand
Remove fan speed control connector from fan assembly and wedge it between the fan and the fan plastic cover as shown
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Reset appliance.
Measure for DC voltage across the red lead (removed fan connector)
and terminal 2 (blue) neutral main terminal block.
Expected voltage 7.5 Vdc.
Note:
Voltage will only be present until the boiler returns to lockout.
Reset as necessary to complete the test.