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Drain Hot Water tank during non-use

Dec 1, 2020
CAL 27 Illahee / Brownsville WA
My Cal 27 has an old hot water heater that works on 120v only now. It had a heat-exchanger for engine coolant but the diesel died in 2006 and I have removed all the old hose and crap the PO left behind.

The boat sits on a mooring behind my house for 6 months of the year during the sailing season. The other half-year is at the marina where I have shore power.

I have a plumbing problem where the fresh water pump never stops running. I've checked all the lines, etc. and am ready to bypass the hot water tank to see if the pump with the expansion tank stops running when this "tank" is out of the loop, so to speak.

Given the above, my question is should I set up the plumbing with ball-valves to enable me to use the tank when I might have access to AC but remove it from the plumbing circuit during the summer period. The tank is 6 gals or less I believe based on the size of the tank.

Leaving water in the tank for 6 months seems like a bad idea, so draining it seems logical. Is it though?

The hot water tank is inside some type of SS "box" where the 120V cable enters and there are the former engine heat exchanger ports and the current water system connections. There is a pressure relief valve near the top, but no draining port. I'm tempted to pull it out and investigate it on the garage work bench.

Costco 16 oz water bottles keep me sailing but that not what the world needs long-term.

Thoughts ?
May 17, 2004
Beneteau Oceanis 37 LE Havre de Grace
Many boats have a bypass for the water heater allowing the hot water lines to be winterized without filling the heater with antifreeze. I guess what you’re proposing is about the same. Personally I probably wouldn’t bother emptying the tank- I would just run the hot water tap sometimes instead of cold to cycle the water through it. But I could see it either way. As for the pump running continuously - if you’re not seeing water leaking from the tank then my guess is the tank isn’t the problem there, assuming you’re waiting long enough for the tank to get filled with water. The pressure switches in those pumps sometimes fail, or the diaphragm or internal valves could be weakening preventing enough pressure from getting built up.
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Jun 3, 2012
Hunter 33 Steamboat Wharf, Hull, MA
The stainless steel box is full of insulation surrounding the aluminum tank. No real need to open that.