[NWH]

I also had this same problem and it was all down to the outlet on the tank for water being really blocked up with gunk etc,the pump was cycling turning on and off like it was trying to pump. I got a coat hanger and cleared the tank elbow and it worked as good as new,I had a brand new pump waiting in the back of the van to fit but thought I'd give this a try first and it worked a treat.