De Dietrich Error Code?

Hi

I have De Dietrich Washer/Dryer LZ 961 E1 which keeps displaying the error code for a blocked drain hose/blocked suds pump. However I have removed the hoses flushed them through. Cleared the suds pump of some fluff, put it all back together and started the program again, all fine then the error comes up again, not always in the same program position.

Sometime I can hear what sounds like the pump getting stuck but I have observed it working both before and after.

I have had two "Engineers" out to repair it both of whom said "no idea m8" not worth repairing, charged me a call out and left!

Help please....
Dave