Samsung P1253 e5 error (not the filter)?

I have a samsung p1253, it had a new pump about 8-9 months ago when the impeller failed but now it has stopped pumping out properly again.

when trying to do a spin cycle it will get to 9 mins on the display and stay there for ages before finally showing the 5e error, it seems to pump out to a certain point and then stop.

we have had the machine apart and made sure all the hoses etc are not blocked but still the problem persists. The only time we have got it to work fully was when we had the waste water pipe below the drum level leading us to suspect the pump although it seems in fine condition (and does pump out a little).

I am totally out of ideas as to what to try next and dont really want to spend £50 on a new pump when im not sure thats the fault. any help would be greatly apreciated.

thanks
james