Zanussi WJS1665W Washer Dryer?

I am getting Error E20 on the machine and it won't enter the spin cycle. as the water will not pump out, I think its the pump as I had the same problem about 18 months ago, it was fixed for circa £125.

Now I have seen compatible pumps for sale for about £30, how would I go about fitting into the machine? I would be grateful for any replies - thanks!