Had one of these for about ten years usually very good if your handy try turning of all the water in the house mains and open down stairs taps so it drains there will be some left in the pump so have old towells to hand then slowly undo with large grips the hoses on either end pull these away from the body there should be mesh filters inside the ends of the hoses these may be blocked hard water areas suffer this or maybe just silt muck etc you can clean these but easier to replace only cost pennies plumbers merchants stock these and usually give you good advice good luck
Paddy notplumber
January 2009