AEG OKO Lavamat Turbo?

Does anyone know how to check the water pump on this machine? We are getting the E20 code and have checked the pump filter at the front of the machine and it is clean. The machine will not drain when the cycle moves to rinse. I've looked inside the tube where the filter fits and it is not possible to see the impeller due a) to it being filled with water (not clear) and b) I reckon the impeller is not visible anyway due to the curved nature of the pipe which the filter fits into.

It is probably the pump I'm guessing but wondered if there is a way of testing it before I go the whole way and change it.

Cheers.