Once known as Hartley18
Join Date: Aug 2007
Location: Melbourne, Australia
Thanked 85 Times in 85 Posts
Rep Power: 11
Diaphragm pumps have rubber flappers on the inlet and outlet side of the round bit (called check valves).
If you can't find any obvious problems with the hoses, it's very possible some rubbish has got though your filter and jammed under one of these - it doesn't take much. You'll have to take the diaphragm off to check it (just undo the hose clamp), but make sure you put it back nice and tight or it won't seal.
A bad day on a boat beats a good day in the office