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Old 10-17-2018, 09:38 AM   #1
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Water Heater Question

Good afternoon.

Just before starting to camp, I installed a bypass kit so I am not sure how the water heater worked before installing. What I have noticed on my camping trips is that when I turn on the cold water, I get hot water first before it goes cold. If I want cold water, I have to let the water run about 15 seconds or so (guestimate) before getting cold water. Is this normal?
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Old 10-17-2018, 06:34 PM   #2
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Well it should only be camper temp the water line are separated only cold goes into the heater tank from the bottom then on to the hot water piping from a separate line so if either valve is closed there should be no hot water flow. It maybe possible that the valve for the hot water is off but then you would get no water at the hot taps.
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Old 10-17-2018, 08:03 PM   #3
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The temp of the water from the cold water tap is normal temp first then scalding and then normal temp for cold tap. I do get hot water from the hot water taps.
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Old 10-18-2018, 08:14 AM   #4
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Did your kit have two valves?
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Old 10-18-2018, 08:34 AM   #5
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Did your kit have two valves?
Yep
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Old 10-18-2018, 03:22 PM   #6
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Check your outside shower/faucet if equipped. Make sure the taps are closed. On one of my units, if the outside shower head was closed, but the taps were open, the hot water cycled into the cold water line. I would also check the inside shower taps and shower head as well.
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Old 10-18-2018, 03:56 PM   #7
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I don't have an outside shower but I will check the one inside. Thanks!
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Old 10-18-2018, 06:50 PM   #8
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Yeah that is possible too if the shower taps are on and the switch on the shower head is off even in the indoor shower.
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Old 10-18-2018, 08:40 PM   #9
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Does this problem happen at both the kitchen sink and the bathroom sink or just one of them?

The actual faucet may have an issue where it is mixing the hot into the cold.

OR

There is another possibility, you mentioned you got scalding hot water after a short duration of cold. The scalding wording triggered this thought process.

Do you turn on the water heater and leave it on all the time until you are ready to leave camp?

Do have a temperature gage or thermometer that can be read how hot the water temperature will get? The heater should be creating 140F. Which is really hot, but if it is creating 160 or worse 180 then that changes the thermodynamics of the heater and the piping setup. It might even be doing it at 140F pending a few things.

This is what I am thinking. There is supposed to be an air pocket formed in the top of the water heater. That air pocket will naturally form when you fill the piping and heater with water the first time. The air pocket creates what we call a "cushion" for expanding hot water. When you heat water the water expands. The air pocket allows the expanding water expand into the air pocket space and not drastically increase the piping pressure.

If the air pocket has dissolved (it happens, not if but when) and the water heater is heating, then the expanding water has nowhere to go, so it starts increasing the pressure in the piping tying to expand out into it.

"If" your cold water supply that feeds the bottom of the water heater has a very short pipe to the main cold supply line, then the expanding water pressure and the excess heat backs up by convection out into the cold water piping. It will sit there hot in the cold water piping until a cold water faucet is turned on. When the faucet is opened, a slug of cold water downstream of the water heater will flow out the faucet, then the heated slug of hot water that backed up from the water heater, then it will be followed with cold water coming in from the upstream supply. That sounds like what you are describing.

To sort that out,

1. Tell us if the heater is on all the time from start of camping until the end of camping.

2. See if you can measure the hot water temp to see how hot it gets.

3. Tell us about when and how you fill the water heater? At camp after you filled up the fresh tank or hooked to city water. Or you had the heater filled from the last campout and did not drain it between trips. Trying to figure out when the air pocket in the heater formed in relation to the specific time this event happen.

If I concluded the issue correctly on how this occurs, your water heater might be too hot creating excess thermal expansion OR you totally lost the air pocket in the heater or both at the same time.

Hope this helps

John
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Old 10-18-2018, 10:03 PM   #10
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Quote:
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Does this problem happen at both the kitchen sink and the bathroom sink or just one of them?
Yes, I believe so. I used the kitchen sink more than the bathroom sink.

To sort that out,

1. Tell us if the heater is on all the time from start of camping until the end of camping.
I light it and leave it lit the whole time camping. I can try only lighting when we need hot water this weekend.

2. See if you can measure the hot water temp to see how hot it gets.
I will have to do this sometime this weekend.

3. Tell us about when and how you fill the water heater? At camp after you filled up the fresh tank or hooked to city water. Or you had the heater filled from the last campout and did not drain it between trips. Trying to figure out when the air pocket in the heater formed in relation to the specific time this event happen.
I hook to city water. I try to drain at the campground. Less weight to tow. Otherwise I drain at home. This is for each trip.
Thanks.
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Old 10-18-2018, 10:43 PM   #11
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OK good info,

Yes try and see if you can get the water temp. It may be way over heating which would aggravate the thermal expansion issue.

Since you drain the water heater each trip (a good thing) then the air pocket will reform by just filling the system.

Do you have a pic of the cold water line feeding the water heater? I thought I saw this somewhere before on yours. If the tube feeding the heater is very short in length and the cold water supply keeps on going to something downstream like another faucet etc, then the thermal convection up that little pipe may not take much to heat the cold water in pipe after the short inlet pipe. That and the heater being on all day. Being on all day up to full temp it has time to thermally convect. If the heater is off, it will not convect as much or as fast as it will cool down some. If the feed tube is long enough that may slow down the heat convection too. It may be that shutting the heater off after use will solve the issue as there is not enough time to have the heat convert up the short pipe. But still get a water temp reading as if it is way over heating that is not good either.

If you have the heater on all the time and it is heating too hot, that can aggravate the issue. I thought you had a newer water heater but I do not recall if it is electronic ignition or a pilot light all gas system. If you are on the electronic, then it is easy to flip it off and then turn it on 20 minutes before you need it. If is an all gas one, it is a little more inconvenient to go out and light it each time. Since ours is electronic we may have it on for a few hours around meal time but then shut if off unless we need it.

I have had ours loose the air pocket and the pressure built to 150psi in the system which tripped the safety relief valve to weep. We can loose the air pocket by towing with the heater full from camp to camp when we do a long trip. My water pump will start banging big time when the air pocket is lost. It can't jam the water into the system as there is no place to expand into. I have gotten to the point of knowing when it will loose it and on those travel days when I get to camp the water is cooled down from the long tow. At camp just as we are setting up, after shutting the pump off and opening a faucet to drain the pressure, I then drain down the heater by about 2 quarts and with the relief valve open it will take in fresh air. Then close the drain and safety valve and let the pump build pressure. The air pocket is reformed. I have a drain hose and valve so it is easy to do. And I know you added one too. I'm just mentioning this so you know if it happens to you how to get the air pocket back.

Hope this helps.

John
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Old 10-19-2018, 04:54 PM   #12
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OK good info,

Yes try and see if you can get the water temp. It may be way over heating which would aggravate the thermal expansion issue.
Will do.

Do you have a pic of the cold water line feeding the water heater?
Here is a picture of the bypass kit installed.
It could be that I have something set wrong but I don't remember having this issue with the first trips.

Thanks.
Attached Images
File Type: jpg WaterHeaterBypassKit.jpg (79.6 KB, 27 views)
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Old 10-19-2018, 06:06 PM   #13
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I would double check the flow orientation of your new bypass valves. Water should go up the white hose (and not into or out of heater when winterizing. It should not go in the white hose at all in normal use. Hope this makes sense.
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Old 10-19-2018, 06:44 PM   #14
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Having hot water at the hot taps kind of means the valves are correct. I suppose it's possible the hot side valve is not completely closed and bleeding some hot water into the cold side until the cold overcomes it.
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Old 10-19-2018, 09:00 PM   #15
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It seems like hot water is being siphoned back into the cold water lines.
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Old 10-19-2018, 09:57 PM   #16
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Having hot water at the hot taps kind of means the valves are correct. I suppose it's possible the hot side valve is not completely closed and bleeding some hot water into the cold side until the cold overcomes it.
I will check that as well.

Thanks!
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Old 10-29-2018, 10:54 PM   #17
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I checked the taps and valves on the bypass and all looked proper. I could not find the thermometer and all of the others in the house don’t have the capacity to measure high temps. This may have to be put on the list for next season. Hopefully, I don’t forget. The memory ain’t what it used to be.
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Old 10-30-2018, 07:29 AM   #18
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If you want to check temps your best bet would be an inferred hand held one something around $30 it's a point and shoot no direct contact.
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Old 10-30-2018, 08:36 AM   #19
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If you want to check temps your best bet would be an inferred hand held one something around $30 it's a point and shoot no direct contact.
I will look into it. We have some warm weather coming next week so I may be able to fill the tank and check.

Thanks a bunch.
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Old 11-01-2018, 10:54 PM   #20
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This very good pic of yours helps tell a story.



The brass all metal bottom bypass valve can conduct heat easier then an all plastic bypass valve. But that is only part of the issue as it alone is not the issue.

Mainah's point about a possible leak through the bottom valve leaking, or the top and bottom valve, made me think even harder if that could cause the problem. And then Jim's comment about a siphon going on.

They are really good thoughts but I'm not thinking they are the issue. Those laws of physics tell us, there has to be a pressure difference (pressure drop) of some level between the upstream source and the downstream area of flow in order for a liquid or gas to flow.

The heater just sitting there with no faucet open or the system is not leaking water out somewhere else, there is not a pressure difference across those valves to allow flow. The pressure is equal in the entire system. With no flow the hot water in the heater cannot flow backwards into the cold water line on the bottom.

But... heat can travel by convection through an object that can conduct heat. The brass valve and the water itself in the valve can transfer heat given enough time with cold water on one side and hot water on the other side.

In this case it takes temperature (more is faster) at certain time (long time) to create enough heat convection to heat up the cold water sitting in the cold water pipes just before the cold water enters the brass bypass valve. That pocket of hot water once heated then travels up and down the cold water pipe with cooler water ahead and behind it.

Once the faucet is opened, the hot water pocket heated in the cold water piping then comes out the faucet and can be scalding as it can be whatever the water heater is. Even if the water heater is working at 140F like it is supposed to, that is hot scalding water. It can get worse scalding and happen faster if the heater is overheating the 140F.

If you want to prove out this concept, fill the system with cool water, turn on the water heater and let it sit and cook all day long, even over night if you want to. Measure or carefully feel the gray cold water pipe by the brass bypass valve at the start of the experiment and then about every hour thereafter and record the info.

If the gray cold water pipe starts heating up that feeds the brass bottom bypass valve, then you know the heat convection concept is going on. This same heat convection is occurring on the top hot water piping too just we do not notice it as we expect hot to come out. Even the white bypass hose will heat some given enough time. The piping closer to the heater will be hotter then further downstream. And over time, it too will change to become hotter up to the point of equilibrium with the water heater as time passes.

This blast of hot I'm assuming will only happen once when the water heater has been on a long time (hours worth) and it's the first time you opened a cold water faucet. Once the blast is over, you can open and close the cold many times in a short time period (less than an hour) and the issue not happen. A leaking bypass valve would create the issue all the time.

Using the infrared gun Mainah was talking about will work good for shooting temps on the brass valve and piping. It can also be used on tires, brake drums, bearings and even your frying pan temperature or the roast under your grill hood, LP gas level in the tanks and other things around the camper. Harbor Freight has one and a web search can find other cheaper ones too. They are not as accurate as really expensive ones but are good enough for a camper setting.

The only way to stop the heat convection practically is to change the time factor and or the water temperature difference in the water heater. If you turn the water heater off for long periods of time of non use, then the water cools down in the heater and cannot convect as much heat as fast. The higher the temperature difference between hot and cold the faster the heat convection process occurs.

What ever you try, please report back. Curious on this one if I concluded the problem correctly.

Hope this helps

John
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