Zanussi pump problem

Have a 4 year old 1200 jetsystem washing machine (model no. WJD1257W) - out of warranty.
The problem is that water is not draining during a wash cycle and I end up with an E20 error message. Lowering the drainage pipe to the floor allows the water out so I think the pump is bust.
How easy is this to fix?
Many thanks
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