Zanussi WJS1665W - does the Drain Pump need replacing?

Hello.

We have had our Zanussi Washer / Dryer for over 10 years now. I clean the front filter on a regular basis and run a maintenance wash.

The other day the drain pump started, made a fair bit of noise then stopped during a Drying cycle. Having repaired the machine a few times now I guessed from the location of the sound it was the Drain Pump. This was the 1st time that this ever happened.

I put the machine on it's side and opened up the pump. No blockages visible and nothing in the main drum pipe going to the Pump or the pipe leading out from the Pump. Motor and Impeller looked OK and I cleaned the thermal cut out switch under the white plastic housing over the coils (even though it did not look dirty).

The Impeller did come straight off the main body of the pump. Not sure if it is meant to do so? Is it broken...?

Machine then worked OK through a wash and drying cycle and today the Pump is back to where it was a few days ago.....

The Daignostice Function on the machine is giving me a E91 code.

Please help.

If it is a broken Impeller, I can easily replace the Pump. If it somethinf else then any guidance wold eb greatly appreciated. Thanks!