05 Mk11 Octavia estate. When fan is turned on fuse FC4 (5A micro fuse) blows. This is one of three fuses that supplies the heater control panel. The other two fuses are OK. Tried replacing heater control panel, still blows fuse. Any ideas please.

Looks like that fuse may supply a few different things. Automatic anti-dazzle mirror, refrigerant pressure sensor, heater control unit and climatronic control unit. Possibly a fault in one of the three you haven't changed, that puts more stress on the fuse?

Inspect the high pressure refrigerant sensor (G65) connector as a first guess, think I've heard of problems with those and water ingress?

Due to the age of the car it's possible the fan motor brushes are worn out and require replacing.

 

Or motor is somehow jammed.