Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Remove the wing nuts from the fan and slacken the grub screw from the injector pipe
Lower the fan into a position so that the impellor is visible
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

WARNING - STAND CLEAR OF THE BOILER DURING TEST
Apply a demand and observe the fan impellor.
Note:
1. Before reassembly check the integrity of all
disturbed gaskets and seals and replace as necessary.
2. Upon reassembly all disturbed joints should be checked for gas tightness.