Re: Roadtrek low city water flow
Check the water heater for gunk by pulling the external drain plug. You might as well replace the sacrificial anode if it's almost gone (or completely missing) while you've got it out. I would also pull the aerator and screen off the sink faucet head to see if any calcium deposit comes out before the flow slows or stops. If it's not some big chunk of calcium stuck in the sink faucet that falls out, then you could try adding some vinegar (maybe a cup or more to a full fresh tank?) to the fresh tank to try to break up or dissolve any calcium pebbles (deposits) that might be loose, and are getting picked up by the flow, and then plugging some bend or fitting along the route to the kitchen outlet. You might have to let it sit with the vinegar for a day or two, or drive the van to get it sloshed around a bit, then let it sit.
I don't think the vinegar will cause you any other problems with your plumbing, but I can't be absolutely sure. Perhaps others with pre-PEX plumbing might be able to provide any caveats regarding that. Once the problem is fixed, just rinse and sanitize your fresh water system like you would if you were de-winterizing.
Is it just the kitchen tap, or all the water outlets? Does it seem to happen when hot water valves are opened, or does it matter? How is the flow from the toilet flushing process around the bowl rim? I had a badly calcified anode rod in my water heater, coupled with a badly plugged water pump filter, that slowed the flow to my kitchen tap and the toilet flushing water. After adding the vinegar and waiting a day or two, I saw all kinds of calcium bits coming out of the toilet water feed pipe, during flushing.
It's one of those things that may take some perseverance to clean up. I suspect calcium deposits from the water heater has been dispersed through the system and is causing the problem, although good flow using the water pump alone does put that theory at risk. I guess I'll assume there isn't water flowing out to ground, when you switch to shore water? It starts flowing strong, then slows and stops, so it sounds like an intermittent blockage in a pipe or fitting somewhere, but I can't explain the good flow from the standalone water pump.
Maybe this diagram of a typical RV water/plumbing system will help ring some bells.
It's not a sprint(er) (unless you make it one), it's (hopefully) a marathon.
RV - 2018 Navion 24V + 2016 Wrangler JKU