Assuming it was faulty, how do you know that the seller knew anything about it?

Unfortunately that is a risk you take when buying second hand. In the UK, the seller is under no obligation to do anything about it unless you can prove that he purposely misled you (e.g. if you found a manufacturer's inspection note in the box mentioning that it needed some work and the seller told you it was perfect). If you want a guarantee then you need to buy new, or from a business that offers a guarantee. Even so, I would guess that the guarantee might only cover the repairs to the turbine.

Unfortunately, with the information presented here, you cannot place the blame anywhere; it is just one of those unfortunate things.