Set Appliance State:
Mains Power Off
Set Multimeter to AC Volts 
Turn Hot Water Tap On
Boiler ON/OFF Switch OFF
CH Temperature Selector OFF
DHW Temperature Selector to Max
CH Temperature Selector OFF
DHW Temperature Selector to Max
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Boiler ON/OFF Switch ON.
Allow Fan to run and Burner to ignite and run for 4 seconds.
Measure Mains Voltage across the Fan at connection 2 (live-red wire) and connection 1 (neutral-black wire).
Allow Fan to run and Burner to ignite and run for 4 seconds.
Measure Mains Voltage across the Fan at connection 2 (live-red wire) and connection 1 (neutral-black wire).
Isolate as per TOPs P4
and refit as necessary