No offense taken at all chuck I said I’m open to ideas and I meant it.. Swapping the valves is an option..but they are for sure plumbed in correctly.
And if one side was closed off the boiler would for certain go out on low flow or high limit. They are quite sensitive in that regard
Yeah, I figured it was piped in right. Just a thought. It's not your job to solve the electrolysis problem if there is one, only to stop it from damaging your pump. An easy way to do this is to attach ground clamps around piping in and out of pump and install a ground wire parrallel to pump. Contrary to what some people think, parrallel circuit of different impedance won't share loads. Less impedance path will carry all currents which will be your ground wire around pump. If just as a experiment, looking at your soldering job, you wouldn't have any problem soldering a #10 solid copper wire to each side of pump piping for a jumper. Is there a way to throttle discharge slightly to reduce gpm flow thru pump? This might reduce cavitation or help diagnose problem. Pump may be of size to be able to move more water than suction line will provide. I have had to trim centrifugal pump rotors in a lathe before for this reason. Are the nameplates of both pumps the same GPM rating? You mentioned they had different impellors. the bad one isn't a higher rated GPM is it?
