Boiler error code?

I have just read the manual - the external probe you mention is an external temperature probe fitted outside the premises - but it's optional and you say that you don't have this option.

The Error Code E08 says that there's a fault with something that your boiler does not have so clearly the fault shown is a phantom - the electronics are playing up.

The manual also says that the E08 fault can not be reset.

I think you need a service engineer.

Good Luck...
March 2017