Boiler fan not turning off

[ausfhrt]

I have a Worcester Bosch Greenstar 15i condenser boiler which is about 13 years old. There is a separate hot water tank.
Recently the fan in the boiler has started to stay on all the time. My usual engineer took a look at it and advised me to contact the manufacturer. I then had an engineer from Worcester Bosch come out. He spent quite some time takeing the whole thing apart and changed a few parts. In the end he told me the boiler hadn't been installed correctly as there should be a wire from the hot tank to the boiler. I was puzzled by this as the boiler and tank were installed 13 years ago when the house was built, and has always worked fine until now. Strangely, it worked correctly when he left with the fan turning off again. Until this week, when the fan started to stay on all the time again.
Any ideas what the problem could be? Having had 2 engineers look at it, I can only assume everything has been checked quite thoroughly.

 

[ShaunCorbs]

S plan or y plan ? And do you have the engineers report eg what’s missing ?

 

[ausfhrt]

Thanks for the reply. I'm not sure what you mean by 'S plan or Y plan'.
The notes Worcester Bosch have from the service engineer state: Link left between LS and LR.

 

[ShaunCorbs]

Thanks for the reply. I'm not sure what you mean by 'S plan or Y plan'.
The notes Worcester Bosch have from the service engineer state: Link left between LS and LR.

I’m guessing the installer didn’t have a permanent live so he’s left the link in and used the switch live as permanent so every time the heating is off there’s no desplay on the boiler / pump overrun

Where’s the main heating fused spur / programmer close to the boiler ?