Plumbing pressure and hot water issue after water heater replacement...resolved

General Discussion
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Just for the record and future reference.

I developed a leak in my 4 gallon water heater (110 VAC + coolant circuit) and decided to replace with a 6 gallon Kuma heater purchased via Amazon.

After replacement and some carpentry to accommodate the slightly larger heater, I noted two issues

First, I was getting hot water from the cold water tap for several seconds before it went cold. Bad because when the water is hot it is very hot, esp from the coolant loop.

Second I was getting fairly substantial pulsing of the cold water feed due to rapid pump on off action.

The first issue turned out to be the fact hot water expands and results in pushing hot water back into the cold water feed line this is close enough to my galley faucet feed to result in the initial hot water output of the cold faucet setting.

Hot in cold Solution : installed a check valve in the cold water feed to the new tank. Cold can go in but hot can’t come back…problem solved. No idea why the old tank did not present this problem, maybe an internal check valve?? anyway, the check valve was the key.

Pulsing solution: Purchased a small resin accumulator tank on Amazon (designed for boats/RVs). Installed this just before cold water feed to water heater. Pressurized it and initially still had pulsing. Started to gradually release pressure in accumulator until I saw pulsing drop to zero. Worked like a charm.

Others on the forum have mentioned use of an accumulator to address this problem. They were completely correct as I can attest.

With regard to the Kuma heater there is also a procedure to periodically refresh the air bubble which lives at the top of the HW tank. This bubble is there to accommodate water expansion when the heater heats up. It has to be refreshed every six to twelve months (water absorbs the air over time). If one does not do this procedure the pressure relief valve will drip to release excess pressure when the water heats up. Again, I experienced this issue and can confirm the procedure works to eliminate dripping.

One more note. On my F30 the plumbing system is very basic. I have lines to the galley and the head and they are all all pex tubing, so I could get away with locating the accumulator under the galley sink close to the water heater (where I had some room). Larger boats may need to locate the accumulator closer to the water pump itself, especially if plumbing is of a material where there may be possibility of expansion of the tubing under pressure.

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Good read Mike! When you get time, would you display a pic of your accumulator? …and how did you pressurize it? I installed an accumulator a couple of years ago thinking it would help even out my water pressure as my pump would cycle on way too frequently. Couldn’t see it do any good so I removed it. Mine said it was pre-pressurized to some figure but I had no idea if that was effective. BYW off topic, the new diesel heater with short run exhaust works perfectly ….

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Camino. Yes I will send a pic. I succeeded in placing the accumulator up in the under sink cabinet where it is out of the way of everything, amazingly enough.

With regard to the accumulator pressure. You will probably note a standard tire inflation nipple on the end of the accumulator tank. I used a bicycle pump with gauge to set pressure just below the cutoff pressure of the pump which is 40 psi. This was per accumulator install instructions.

Turns out this was too high because I saw zero improvement in the pulsing problem. I figured what the hell, I’ll just start deflating the accumulator bladder and see what happens. As I did so in short bursts (just like deflating a tire) I could tell the pulsing was starting to moderate. I eventually got to a pressure where the pulsing disappeared completely…sweet. you may know this but the accumulator has a rubber bladder inside which is designed to compress and expand sort of like a shock absorber. I have the same set up with my osmosis water system in the kitchen - much bigger tank though.

One thing I found is that the bladder is so small that just detaching the pump can cause a significant pressure loss. So I just knowingly overfilled it and went to the “try it till you like it” mode.

Meanwhile I imagine the neighbors were wondering what I was doing carting a bicycle pump down to the boat… :rofl:

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Here is a pic of my accumulator location

Here’s a link so you can see what it looks like in more detail

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Backing away a bit for context.

Its a bit of a mess with fan for dry out of water spilled when changing hoses .

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By the way, tell me more about the heater. What does short exhaust mean?

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Mike - ok I’m all in (again). This time I’ll pressurize the darn accumulator tank! I mounted my old one in that blank space by the batteries - and I’ll add I know it seems a fixation, but when things go right with the boat , things are right :). Yesterday out sailing after spending 2 months in the doors and heater , all was good and the boat handled everything well. My wife puts up with me!

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…and shorter exhaust - the first one I didn’t know I could cut the exhaust- so I had 6’ of ss exhaust wrapped around the lazarett- after 4 yrs I had several burn spots on the hull! So new one I used 33” ss exhaust and kept all away from hull and hoses. Seems to work!

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Yes that shorter exhaust ought to let the unit breathe a bit better. Mine is about six feet long but heads straight to the transom with a bump to prevent water ingress into the exhaust tube.

I wrapped my exhaust tube in some fiberglass insulating material and used some ss seizing wire along the length to hold it away from the hull and other heat sensitive items like the bulge pump tubing. I have a small IR gun to take temperatures of various mechanical bits and the exhaust never gets above 200 degrees F so that is pretty good I think.

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Re the accumulator. It should have max pressure printed on it somewhere. Mine is 125 psi. Never got anywhere close to that, but, obviously, you want to be aware so you don’t blow it up.

Then just let a little air out until you hit - or hopefully hit - the sweet spot. I did this with the faucet open so I could see when the pulsing decreased and finally went away completely

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Right about the IR gun - use it all the time. Pic shows new install of exhaust. On the accumulator tank - making sure I get it right - hose from water tank to water pump “in”, water pump “out” to accumulator tank “in”, accumulator “out” to boats water system…? Thanks

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With my accumulator water can come in and out either way. Use care, I suppose some might be directional with a check valve or some such.

So one side to cold water out of pump. other side to HW tank cold input. That means accumulator is in line with cold water from pump.

I did this right at tank but you will do it at the pump I think, same difference. However they do recommend placing it close to pump so yours will be in accord with instructions. seems to work either way so long as you don’t have a big system.

It will be interesting to see if you can get it to work properly.

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Ok, accumulator tank in, psi at the tank 36psi- seems ok at faucets. Tank is 1 liter, I think yours may be .75 liter. Also varnished steps…saw your steps and got jealous! LOL. … no sail today.

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