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Old 07-03-2017, 09:26 PM   #1
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raritan water heater

Hi to all,
We have a weird problem with our hot water heater(raritan), actually the cold water. This just started happening. When we turn the cold water on it starts cold then within a few seconds the water becomes hot, very hot. We've let it run to see if it would cool down but it doesn't.
Any ideas?

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Old 07-03-2017, 09:35 PM   #2
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Assuming no work has been done on the plumbing, I think your cold line must be blocked and the hot tank is back feeding into it. Perhaps at a mixing valve?


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Old 07-03-2017, 10:22 PM   #3
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Mr. GB. Do your water lines run through your ER? Our "cold water" is in fact hot after a day's travel due to the routing of the supply lines in, out and around our ER.

Ah. Just re-read your post. This is a new phenomenon for you. Forget about my comment above...
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Old 07-03-2017, 11:01 PM   #4
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I suggest you give Raritan a call...800-352-5630
© 2020 Peggie Hall
Specializing in marine sanitation since '87.
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Old 07-04-2017, 09:13 AM   #5
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The cold line doesn't run through the water heater so most likely hot water from the tank is backing into the CW line. I'd try eliminating possibilities. Was the boat winterized? If so was all air bled out of the lines when starting the system back up this year? Any valves closed? Bad check valve or mixing valve? Does the problem occur at every faucet? (If not, that will tell you where the problem 'isn't')
+1 to call Raritan but you could first disconnect power to the heater and go through the whole winterizing / restart process.
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Old 07-04-2017, 09:20 AM   #6
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If you have no airspace in the water heater or an external expansion tank, when the water in the water heats up it expands. This is like the engine in your boat or car. As the coolant in your boat or car engine expands, it's pushed out through the radiator cap to the overflow tank. For the water heater without an air space or expansion tank, the water can be pushed back into the pressure tank of your fresh water system. I had this problem and solved it with a check valve and an expansion tank. This may or may not be your problem, but it would explain hot water in the cold water line.

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Old 07-04-2017, 08:23 PM   #7
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If the water stays hot like you say, it's likely you're seeing a back/cross feed. Expansion issues typically will feed hot water for a minute or so, then it'll cool down. Most marine water heaters are installed with a check on the cold supply line.

Fortunately, because of the temperature not being where it's supposed to, it should help in troubleshooting. You'll have to be methodical, and step through every line. Start by duplicating the condition, then work through the plumbing and note each place the cold water isn't cold. I'd start at the water heater inlet. If there's a check valve, there's little potential for back feeding through the check valve. If it's hot on the side of the check furthest from the water heater, the check is probably blocked open. If so, remove it and free it up. If it's calcium buildup, just dunk it in some muriatic acid for 15 minutes until the calcium's gone. Even if there's backfeeding, unless there's a source for the cold supply to jump to the hot side somewhere in the system, it's not likely to stay hot very long.

If the check isn't hot, then follow the cold line and see where there's a hot spot. If any fixture has a hot hot line, and a hot cold line, suspect a failed mixing valve that's cross feeding hot into the cold. It's unusual, but possible. If there's a deck shower with a mixing valve, check to see if the hot/cold valves have been left open and the shower head valve is keeping it from flowing, that's a good spot to check.

Be methodical, be thorough. Check every fixture. The one you overlook will be the one that's the bogeyman!
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Old 07-04-2017, 09:55 PM   #8
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I put a check valve on the cold line into the heater. As the water heats, it expands and has to go somewhere. If all the taps are closed it flows up the cold line to any expansion tank and even back to the tanks in some systems. Check valve usually solves the problem.
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Old 07-10-2017, 09:36 AM   #9
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Thanks everyone. I'll post when the problem is solved.
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Old 07-10-2017, 09:43 AM   #10
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Does this phenomena occur at all hot/cold outlets or just one in particular?
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Old 07-10-2017, 01:11 PM   #11
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raritan water heater

I have this problem in the aft head sink. I thought it was solar heating in the machinary space, but alas, it was caused by a crossover in the shower that is teed off before the sink connections. I have a watersaver switch on the shower head, and if you flip it to the off position and forget to turn the shower faucet off after a shower, it causes the crossover when using the sink. It took awhile to find the culprit, but now I can stop and start the phenomenon on demand
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Old 07-11-2017, 11:25 AM   #12
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I haven't been able to work on this yet. It could very likely be a check valve problem.

It does occur on all faucets.

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