Can anyone help? I have a sanisuite system and now when the loo is flushed the bowl fills up and the pump is slow in switching on, i have checkedthe non return valve and for blockages all seems fine.

don't know about sanisuite, but in our last house we had a saniflo unit (presumably much the same) which serviced the loo, shower and basin, and it showed the same symptoms as yours. I had to replace the rubber diaphragm which sits at the bottom and activates the pressure switch - it had become mis-shapen.