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Old 04-29-2013, 03:04 AM   #1
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Default Pulsing hot water

Please help! All of my faucets, when turned on hot, go hot - cold - hot - cold - hot - cold, and so on. It changes about every 2-3 seconds. Any clue what it might be. The water is plenty hot. This is happening on a 1999 SCA 4100 Sport Yacht.

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Old 04-29-2013, 02:20 PM   #2
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I've never heard of such a thing. It kind of sounds like when the lower heating element of a standard residential hotwater heater kicks out.
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Old 04-30-2013, 12:20 AM   #3
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Sounds very similar to my problem. I have been trying to figure this one out. Mine seems to be sucking air, which causes bubbles in the lines(very apparent when I was blasting out the pink this year).

Then my hot water pressure drops to a trickle.

I just can't figure out where the problem starts.
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Old 04-30-2013, 03:54 PM   #4
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rcswando, you're not recommissioning with the hot water tank running, are you?

What you're describing sounds like air in the system, which happens. Once all the air works out, that should stop. While recommissioning mine, I will get good flow, then weak or no flow, then foam, then good flow again. The OP sounds like he is getting hot and cold water alternating.
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Old 05-01-2013, 02:47 AM   #5
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Fellow Boater,

I will try and explain with as much detail as possible. I have only had this boat 6 mos and used the hot water plumbing very little. The I know the hot water tank works well because the water gets really hot when any faucet is turned to hot. I am operating the system on a freshwater pump, not a city water hook up. The freshwater system has one of those pressure bulbs that has been checked and works properly. The pump is a 40 psi, I think 2.8 gpm. And I was told that it was brand new when I purchased the boat in November. The hot water and cold water goes back in fourth with the pump. When the pump is running the water is cold and when the pump is off it gets hot. I hope I have that the right way. Thanks for any and all help.

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Old 05-01-2013, 03:42 AM   #6
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Sounds like you are over powering a splitter valve somewhere. It appears to be a pressure issue. But it's odd you would get any water pressure with the pump off.



You may have a heating element going bad that is over heating the water in the tank and causing it to build pressure. try replacing that.. it should be easy and cheap.
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Old 05-01-2013, 03:32 PM   #7
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I don't see how an element going bad would cause this issue. I also only think these small tanks only have 1 anyway. The way they all work is cold water flows into the bottom of the tank. If the inlet is at the top, the pipe runs deep inside the tank and stops just before the bottom of the tank. The hot is pulled from the top of the tank. If it too is on top next to the cold inlet, it just has a short pipe going inside the tank. This ensures that as you use it, cold fills the bottom, heat rises and only hot leaves the tank.
Those DC pumps do build pressure and normally do not run constantly when water is on. It should have a high pressure shut off and a low pressure engage switch. So once x amount of pressure is built up, it shuts off until the pressure falls below x pressure. So it is common for them to run, stop, run, stop, etc... while using water. The pump should be just after the holding tank and before where the water splits off to the water heater or cold pipes feeding the faucets.
I would question if you have a water heater bypass kit installed on the system? They are common and very useful when winterizing so you don't have to fill the water heater with AF.
I have seen some with diverter valves on both the hot and cold side. I have seen some with diverter only on cold and a 1 way valve between the hot outlet and the pipe (short valve that looks more like an adapter than anything).
It could be that when the pump is running and the pressure is high, it is forcing water through a diverter valve that is faulty or partially open and when the pressure starts to drop, more hot gets through.
Sounds like a bit of a stretch but I can't think of anything else that would cause it to go cold like that.
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Old 05-02-2013, 02:15 AM   #8
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I really appreciate the trouble shooting you guys are providing. I am pretty sure there is not a bypass on the water heater. I have got down into the mid hull area and checked it out. There is a hose coming off each inlet. I read on an RV site that a guy with a very simular issue solved it by putting a variable speed pump in. I do have a new pump, could it be there wrong type? I had a houseboat before this cruiser and I replaced the hotwater heater and pumps and never had a problem like this. I am curious how this system is able to push hot water to all the faucets when the pump is in the aft stateroom and the water heater is opposite the galley near the forward head.

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Old 05-02-2013, 02:29 AM   #9
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Default Hot Water issue

Fellow Boaters,

Please help! All of my faucets, when turned on hot, go hot - cold - hot - cold - hot - cold, and so on. It changes about every 2-3 seconds. Any clue what it might be. The water is plenty hot. This is happening on a 1999 SCA 4100 Sport Yacht. I have only had this boat 6 mos and used the hot water plumbing very little. The I know the water heater works well because the water gets really hot when any faucet is turned to hot. I am operating the system on a freshwater pump, not a city water hook up. The freshwater system has one of those pressure bulbs that has been checked and works properly. The pump is a 40 psi, I think 2.8 gpm. And I was told that it was brand new when I purchased the boat in November. The hot water and cold water goes back in fourth with the pump. When the pump cycles the water is cold and when the pump is not cycling it gets hot. I hope I have that the right way. Thanks for any and all help.

Thanks,
SunChaser
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Old 05-02-2013, 02:59 AM   #10
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Hmmm, I am no expert in any of this but I can't see how a variable speed pump could help here. Somehow you are getting cold water into the hot water side of the system and that can only happen if they are connected together with 3 way valves (meaning a bypass kit) or cold water is exiting the tank through the hot outlet (meaning poor design or improper mounting angle). The hot side is connected to the cold side but only through the water heater.
So basically you have the water storage tank with a line coming out of it feeding the pump. The pump then pushes water into the cold water pipes. One of the cold water pipes is connected to the inlet side of the water heater and thus pressurizes the entire tank.
This causes the hot side to be pressurized as well as there is nothing in the tank other than an element to heat the water. The water heater just uses the good old "heat rises" rule to let only hot come out the outlet side.
So maybe it is not mounted correctly and the inlet side is not truly on the bottom of the tank and therefore could make it easier for cold to escape the hot outlet side?
if you did have a bypass on it, you would notice it I would guess. My experience here is with an RV and mine is mounted right at the tank. It originally had a shut off valve on the cold inlet side and a 1 way valve on the hot outlet. It also had a jumper pipe connected between the cold side just before the shutoff valve and the hot side just after the 1 way valve. This jumper pipe also had a shutoff valve in it. To bypass you simply closed the shutoff at the cold inlet side and opened the shutoff in the jumper pipe. This redirected the cold flow up the jumper pipe, the 1 way valve prevented it from backfeeding into the water heater and it simply flowed into the hot side pipes only. After 1 season I found that the 1 way valve was bad and was letting AF leak into the water hearer causing me to use about 3 gallons more than I should have. So I replaced that bypass kit with a better, more foolproof system that had 2 x 3 way valves. So now there is a 3 way at the cold inlet and the hot outlet and a jumper between the cold and hot that connect to both valves. So for normal operation, open both valves and it closes the jumper pipe and lets cold into the tank and hot to exit the tank but nothing through the jumper. When both valves are flipped to bypass, cold is redirected up the jumper and into the hot pipes. No water enters the water heater through the cold or hot side.
I can't imagine this system being located anywhere else as that would leave pipe with water still in it. I guess it is possible though??
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