Set Appliance State:

Mains Power Off
Selector Switch to Hot Water and Heating
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

When you turn on the boiler the fan will run on a precheck for approx. 5 seconds then stop.
Turn hot water tap ON.
Does the fan run?
IF E160 FAULT CODE IS SHOWN WHEN FAN RUNS CLICK HERE