Zanussi Washer/Dryer E20 fault?

I have a 5 year old Zanussi Washer/ Dryer ZWG 1472S, its behaved faultlessly up till now, it washes no problem but on a drying cycle after a few minutes it starts beeping & comes up with fault E20, have read up a bit on this so removed & cleaned the filter housing & pump/ another pump sat behind it & all associated plumbing. Both pumps had a large ball of hair/ debris etc in the impeller housing which I smugly thought was my problem, but the fault still remains.
I presume the pump that’s part of the filter housing is the main drain pump, this appears to work well as if I power it up it spins freely & there is no issue with draining on a wash cycle.
But:
What is the pump sat by itself behind the filter housing, it has a hose from the filter & another to the top of the drum, this pump seems to not be working correctly, I removed & tested it & the impeller seems to just go back & forth & not rotate, is it to recycle the water through the drum & if so even though it appears not to be working would it give my E20 fault.
Thanks in advance