Hello all!
Well I finally sorted the pump out. It was crud in the filter!
However, this leads me to another question: When we got the boat, we were told that the water tank needed sanding down and re-painting which we did. The filter was barely getting water through because of the backlog of what I can only asume was rust. Unfortunately we couldn't unscrew to get to the filter, so we ended up putting a screwdriver through the wire mesh and pulling it out. The filter (round clear thing) is in tact but was impossible to open due to many years unattended I expect. The water is now pumping like a dream, but not being filtered. We do though, have a water filter under the kitchen tap. I have been looking around on t'internet to find a replacement, but I can't find anything which looks the same. Has Shurflo changed the design? Also, is it absolutely necessarily to replace this? We've probably had around five full tanks of water go through the system, so would I be safe to assume that when had been lurking in the pipes has gone through the system and now come out?
Hope you guys can help me in this quandary!