I've recently been having issues with the pumps on my 50l BM. The pumps are the blue Vortex ones
.
I bought the unit second hand about 18 months ago and noticed during the last half dozen batches or so, the pumps had occasionally been making rattling noises, especially at 70 + deg C.
During the last couple of batches, the pumps were struggling to push the wort over the top of the malt pipe at the higher temps.
After eliminating other possible causes, and reading about similar issues on the Braumeister forum, it seemed like either the impellers or pumps were going to need replacing.
I spoke to the good folk at Grain and Grape and decided to replace the impellers, being the cheaper option and all. I Also replaced the gaskets while I was at it.
Well after installing them and running the pumps for a for a while, it seems to have fixed the problem.
I'm not sure if the impellers were damaged in any way by the previous owner, I doubt it, as there were absolutely no visible signs of damage on them, or whether they became a bit unbalanced over time.
Fingers crossed that this has fixed the issue long term.