Set Appliance State:

Mains Power Off
Ensure boiler is cool so there is a demand for preheat
DHW temperature control to Minimum (0)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

1. Does the fan run at high speed with No demand present?
2. Set DHW temperature control to Maximum.
Does the fan run before boiler returns to lockout?