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Old 02-07-2020, 11:14 AM   #21
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Why I replaced the check valve with a shutoff valve

The biggest issue I had with the check valve on the outlet of my hot water heater was that when I cut my shower head to a trickle using the water saver button, the water in the shower hose would go ice cold. This was due to the pressure drop across the check valve at low flow.

I removed the check valve - now the trickle stays warm and I get warm water when I turn off the shower water saver button.

I installed a 1/2" shutoff valve in the PEX between the hot water heater outlet and the first tee, so I can still winterize with RV anti-freeze without it backing up into the hot water heater.
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Old 02-08-2020, 06:32 PM   #22
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Hot water heater bad check valves

HOT WATER HEATER – BAD CHECK VALVES

To answer Goodspike's question on how hot water scalding can occur, first you have to experience it. Then you know it’s possible. As for why it’s possible? That's a bit hard to explain, but I think I figured it out.

First, you have to be boondocking. ...Meaning, there is no hose pressure coming in… and only your RV pump will be running (on-off-on) as needed.

Second, it might be necessary for the hot water tank to lose or partially lose that air gap that is supposed to be there so water can expand in the tank. I.e., without the air gap tank pressure will increase to potentially unsafe (HIGH) levels. And this is why you have a Safety Pressure Release Valve; and why you hear stories of hot water tanks exploding. So yes… there is a lot of water pressure that builds up in your hot water tank; and if the TOP check-valve fails then you can’t get rid of the pressure any other way except through the cold water line… which occurs when you turn on your shower valve, for example.

Note: Many people, including myself, have fixed hot water shower temperature fluctuations by purging the Safety valve to remove water in the tank. This re-establishes the air gap. …But when you have a partially stuck check-valve, you might notice your shower handle “sweet spot” (102F) starts to change, even though you can still shower like normal.

MY STORY: For about 3-4 days I was experiencing odd shower water temperature fluctuations while I was traveling and boondocking. And toward the end there were times when all I could get was cold water out of my shower head. That’s when I started to investigate, because I hate cold showers in 40F outside weather or 80F weather:

==> I removed the BOTTOM check valve in my tank and found a spring and the check valve plate barely hanging on. It was destroyed, but it was not blocking the cold water flow into the tank. (And who knows how long it was like that? Probably years.)

==> Then I removed and found the TOP check valve was frozen shut. So bingo: No Hot water was being allowed to pass through. But why was I getting “flashes” of very, very hot water?

OTHER INFO: Your shower valve is a mixing valve, and if you don’t have a hot water source then cold water will come out of the shower head even when you turn the valve all the way to hot. And the reverse is true too.

So the question becomes, how does hot water get into the cold water line? Answer, stuck and/or partially stuck check valves; or a bad 3-way valve, which has been known to fail, but not that often. Remember, your RV hot water thermostat is set at 140F, and most people like 102F showers.

So I have 2 theories on how these no-good check valves cause problems:

A) When the check-valve is barely working it "pops open, then closed, then open" …and the results are bursts of hot water. This is annoying, but probably does not lead to scalding.

B) Scalding is a bit more complicated. It requires the top valve to almost fail completely or completely fail. Why?

Your RV pump is a momentary pump and you know this because you can hear it turn on and off when it reaches maximum PSI. …But if your check-valve is partially or completely closed, then the hot water pressure in your tank is fighting with your pump pressure and when the tank pressure is winning -- then hot water is allowed to enter the cold water line for a certain period of time. Then the line pressure from the pump wins when the tank pressure drops!

This why your shower will run cold for a longer period of time than usual; and then for no reason at all you might have 102F hot water, or you might have very cold water, or you might get nothing but hot water at 140F. And 140F is very hot… maybe not scalding, but it will burn you.

** With a failed Top Tank Check Valve… once a column of pure hot water enters your cold water line, it has nowhere to go but out the cold water side of the shower valve… if you are showering.

CONCLUSIONS

** The hot water tank pressure needs to balance with the cold water pump or line pressure. And when you have a stuck or partially stuck check valve in the TOP of the tank it can’t do that.

** And if you have a stuck (closed) check-valve in the bottom of the tank then no water will fill the tank. ( Which can create different problems.)

** Check valves are prone to failure and I don’t know about you, I hate cold showers, which is the more likely scenario; but I also don’t like getting “flashed” with 140F water either.

SOLUTION TO EVERYTHING

The easiest, cheapest, and most RELIABLE SOLUTION is the drill the guts out of those check-valves and re-use them. Problem solved indefinitely!

Note: As part of your RV emergency kit, you should pick up 2 of those rubber donuts (50cents) that go between your hot water plastic fittings and your check-valve-nipple. These often leak and they are very hard to find on the road.

Happy motoring to us all!
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Old 02-09-2020, 09:58 AM   #23
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Originally Posted by imnprsd View Post
HOT WATER HEATER – BAD CHECK VALVES

To answer Goodspike's question on how hot water scalding can occur, first you have to experience it. Then you know it’s possible. As for why it’s possible? That's a bit hard to explain, but I think I figured it out.

First, you have to be boondocking. ...Meaning, there is no hose pressure coming in… and only your RV pump will be running (on-off-on) as needed.

Second, it might be necessary for the hot water tank to lose or partially lose that air gap that is supposed to be there so water can expand in the tank. I.e., without the air gap tank pressure will increase to potentially unsafe (HIGH) levels. And this is why you have a Safety Pressure Release Valve; and why you hear stories of hot water tanks exploding. So yes… there is a lot of water pressure that builds up in your hot water tank; and if the TOP check-valve fails then you can’t get rid of the pressure any other way except through the cold water line… which occurs when you turn on your shower valve, for example.
You're mixing a two different things there. An air gap (or expansion tank on home systems) is to keep the pressure from getting to be too great on your plumbing system. That's probably particularly a concern on trailer systems. The pressure release valve is more for extreme situations where the water might get way too hot and build up the type of pressure that would burst even a metal tank.
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OTHER INFO: Your shower valve is a mixing valve, and if you don’t have a hot water source then cold water will come out of the shower head even when you turn the valve all the way to hot. And the reverse is true too.
This is correct and where you will get one system overpowering the other if the pressure in one is greater than the other. Note though the issue is pressure, not flow.

Quote:
Remember, your RV hot water thermostat is set at 140F, and most people like 102F showers. [/FONT]
This is the core of the scalding problem. Water heaters should not be set to over 120 degrees due to scalding concerns. I suspect the long term solution to this problem will be class action lawsuits against the RV water heater manufacturers. This video shows a manufacturer add on adjustable thermostat--I suspect that part will become standard with that brand and others.



My unit is new and I haven't tested the temperature yet. But if it's a problem another solution would be a mixer valve to maintain temperature at 120. I'm not sure there's room for that,or thought about how that would affect winterization, but that is sometimes used on home systems where they want to maintain a higher tank temperature.
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Old 02-09-2020, 10:30 AM   #24
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Hmm... millions of RV water heaters sold, with fixed-temp (140 deg. F) thermostats, and we don't see many reports of injury, lawsuits or product recalls. I suspect that means the design is OK.

This post lists the temps for the "regular" thermostat, the ECO (Emergency Cut Off) thermostat, and an adjustable thermostat, at least for an Atwood water heater.

As far as mixing valves go, like check valves they are prone to failure. They are used on some RV water heaters (e.g., the Atwood XT), in an attempt to get more hot water out of a smaller tank. I would not have a mixing valve if I could avoid it.
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Old 02-09-2020, 11:41 AM   #25
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Hmm... millions of RV water heaters sold, with fixed-temp (140 deg. F) thermostats, and we don't see many reports of injury, lawsuits or product recalls. I suspect that means the design is OK.
Hardly, it just means the manufacturers (or their insurers) are ignorant of the risk they are taking.

If you've ever had a house inspected for purchase the inspector would check to make sure the water is not over 120 degrees. Washington state even has a statute on water heater temps (with mixing valves being an exception), and the guidance has been 120 for over 30 years!

https://www.npr.org/sections/health-...ping-burn-risk

I suspect they go with the higher temperature because at only 6 gallons of capacity 140 degree water will create more 100 degree mix water than at 120 degrees.

The potential of scalding from 140 degree water is even greater in a motor home/trailer than in a house for the reasons discussed here, particularly turning the water off during the shower to conserve water.
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Old 02-09-2020, 11:57 AM   #26
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Here's an attorney advertising for cases involving hot water and nursing homes, but the reason I found it is I was searching for the chart showing the difference in scalding times for children/elderly. It's quite shocking.

https://www.mnnursinghomeneglect.com/scalding-injury/

For normal people it's less than 5 seconds to scalding at 140 degrees, but for children/elderly it's 1.5-2.5 seconds!
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Old 02-09-2020, 01:01 PM   #27
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RV hot water heaters with 6 or 10 gallon tanks are set to heat the water to 140 F and I have never seen any posts where someone found a lower temp sensor to reduce this.

I have not tried this, but it might work: Tempcontrol Thermostatic Mixer Valve, $ 22 . Set to 43 C it would mix hot and cold to 110 F. Set to 49 C it would mix to 120 F.

If installed to lower temp of all hot water in the RV, I'd remove the check valve and switch to a three shutoff valve winterization valve set up at the same time. The hot-cold winterization bypass should be on the outlet side of the mixing valve.

I might have tried this, but instead I built a custom controller solution that uses temp sensors, relays, and 12V solenoid operated water valves to manage hot water in my RV. It monitors hot water tank temperature and shuts off the same inputs that the gas and electric water heater switches feed when it senses the water in the tank is warm or hot, depending on how it's set on the control panel. It also pre-charges the hot water line to the bathroom and/or kitchen with heated water, returning the cold water to the fresh water tank. I found around 105-110 F is about the right temp for shower water (warm) and about 115-120 F is about the right temp for dishwashing (hot). With the Smart Water switch off, it goes back to default and I go back to 140 F water.

The concern with using a mixing valve in a RV is the pressure drop across it, given that when boondocking, the water pump pressure is usually only 35-40 PSI.

Control panel and display for what I built and installed in my RV:



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Old 02-09-2020, 02:49 PM   #28
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RV hot water heaters with 6 or 10 gallon tanks are set to heat the water to 140 F and I have never seen any posts where someone found a lower temp sensor to reduce this.

I have not tried this, but it might work: Tempcontrol Thermostatic Mixer Valve, $ 22 . Set to 43 C it would mix hot and cold to 110 F. Set to 49 C it would mix to 120 F.
Nice find. And their "Valve B" looks like it could be setup so that you could have the adjustment knob sticking out somewhere so you could easily adjust.
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Old 02-10-2020, 12:55 AM   #29
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Goodspike: With all do respect, you don't sound like an RV tech, because all your references are comparing an RV hot water tank to a residential 40+ gal. hot water heater.

Just asking: How many RV hot water tanks have you replaced or repaired?

(No b.s. There's no shame in saying zero. After all, what's a forum like this for if not to share our RVing experiences.)

Also, an RV hot water tank needs the air gap as I explained, but you don't seem to comprehend that principle, because it sounds like you know it all from fixing residential water heaters.

My apologies if I'm wrong. ...It's just that you have an authoritarian tone, like you know it all and yet what you say is contradictory to my personal experience.

RV hot water tanks are quirky for sure... but reliable and cheap is the name of the RV game. And sometimes it's as simple as an "air gap" that makes these things work right.

So again, from personal experience, if you don't have an air gap in the top of your RV hot water tank you can... repeat can... experience hot water temperature fluctuations, but not scalding. Usually it's "cold flashes" that are discomforting.

I also would never reduce my thermostat lower than 140F since I would be using more water to take a decent 102F shower when I boondock. In fact, they sell adjustable thermostats and fixed 160F thermostats for those who RV in very cold weather. And I no one I know uses less than a 140F.

Regarding residential homes in the USA, this market is just now seeing some Temperature Compensating Shower Valves on the market, but in Asia and Europe they are common. This regulates temperature vs. Pressure Compensating Valves normally sold by 99% of all plumbing supply store and Home Depot and others.

I just installed a Temp Comp Shower Valve in my home and they are pretty cheap and reliable if you buy them from Amazon. However, Moen, Grohe, Kohler, and others sell Temp. Comp. Shower Valves for a lot of money. Why? ...Probably because they don't want to obsolete the current USA market... since I think Temperature Compensating Valves are superior... BUT ONLY IF YOU HAVE HIGH ENOUGH WATER PRESSURE for these type of valves to work right... which leaves the RV market "out or borderline."

The subject are bad check valves; and like I said: BAD CHECK VALVES... cause problems! And after you experience scalding (140F) coming out of the cold water side of your RV shower valve then you know it’s possible for hot water to back flow into the cold water lines.

...Now it might be true that I did not "theorize" correctly on how hot water enters the cold water side of an RV (repeat RV) hot water system, but it can. ... And I suspect that when you have a check-valve in the cold water line (located at the bottom of the tank) that this check value prevents hot water at 140F from backing up into your cold water side of the system.

... That said, besides installing check valves for the purposes of "winterization" it makes sense the cold water side check-valve prevent hot water (scalding) problems that could... repeat could occur... if you don't have a check valve in place or your current check valve is frozen open. However, this can only happen when a number of factors are present. So in my case, I "gutted" both check valves and I make sure I always have a sufficient air gap in my hot water tank by... 1) Turning off the pump; and 2) I open the tank safety valve to let water run out. And I do this whenever I start experiencing hot water temperature variations in my shower, which only occurs once every season if at all.

To be clear: I'm not advocating you gut your check valves as part of your routine maintenance. Rather, I would wait until they fail; and then "drill them out clean." This will leave you with a standard looking pipe-nibble you can reuse. And that's why I suggest you carry a couple rubber donuts so you can perform this repair in the field yourself. ...Cost 50-cents for each rubber donut(s).

To be double-clear: If I was installing a new hot water tank, I would not use any check-valves because they are so prone to problems. Specifically, when the check-valve fails and you end up with NO HOT WATER... it's a real vacation killer if you ask me!

You know who can clear this up? Hey... Old_Biscuit! Are you still with us? I heard you are or were recovering from some serious illness not to long ago. ...So please send us a reply so we know you are still in the game! ...Can you tell us, how does 140F hot water back flow into the the cold water side of the system? ...And why would it "pulse" hot then cold then hot again? (My theory is that the pressure in the hot water tank is fighting with the pressure in the RV pump, when boondocking, and all other conditions exist. ...Like not have the proper air gap and not having a cold water side check-valve. ...WHAT SAY YOU?


On behalf of many of us who have benefited from you wisdom and knowledge over the years: You have been an inspiration to us all and we miss you!
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Old 02-10-2020, 08:30 AM   #30
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Goodspike: With all do respect, you don't sound like an RV tech, because all your references are comparing an RV hot water tank to a residential 40+ gal. hot water heater.

Just asking: How many RV hot water tanks have you replaced or repaired?
None, but guess what? That quite frankly is relevant to nothing we're discussing. How many transmissions have you rebuilt? That is just as irrelevant.

Scalding doesn't depend on whether you're in an RV or not. And scalding isn't dependent on how many RV tanks you've replaced.

I do know enough to know some of the difficulties of taking a shower in an RV--and even mentioned them above. And I know enough to know that having hotter water in the tank will mean you run out of water later in the shower--and I mentioned that above. But making water an unsafe temperature to avoid running out of hot water is not an acceptable solution to me.

I also mentioned a viable solution--a mixer valve, a solution some RV companies have apparently turned to. The more I think about that the more I like that solution (assuming it works), especially if the adjustment of the valve is readily accessible. That valve could be set at the temperature you want to take a shower on and then only turn on the hot water in your shower. That would actually save water because you wouldn't waste water trying to set the temperature. It could also be adjusted to different temperatures for different people (my wife likes hotter showers than I do). Having only the hot side open may prevent any flow back of water into the cold side when you shut off the flow while soaping up to conserve water.

It doesn't seem like a difficult project, particularly on my trailer where the piping is fairly accessible. As I said, my trailer is new and I haven't tried the shower yet. If it's a problem that will be one of my next projects.
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Old 02-10-2020, 08:44 AM   #31
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The subject are bad check valves; and like I said: BAD CHECK VALVES... cause problems! And after you experience scalding (140F) coming out of the cold water side of your RV shower valve then you know its possible for hot water to back flow into the cold water lines.

...Now it might be true that I did not "theorize" correctly on how hot water enters the cold water side of an RV (repeat RV) hot water system, but it can. ... And I suspect that when you have a check-valve in the cold water line (located at the bottom of the tank) that this check value prevents hot water at 140F from backing up into your cold water side of the system.
I'm not sure how you get from a check valve prevents hot water backing up into the cold side--to drill out a back check valve rather than replace it. That really doesn't seem to follow. Seemingly a better solution would be to look for a better quality check valve (or maybe a water filter--something I'd rather avoid).

I agree with you that a pressure compensating valve probably wouldn't be that effective for RV use.

Here's another thought though. Maybe what is needed is another check valve! One on the cold water run to the shower. The worst place back flow could occur would be at the shower mixer valve. Back flow could conceivably happen at the mixer valve when you turn the flow off at the shower head because both sides are open.
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Old 02-10-2020, 10:04 AM   #32
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I know a fellow who installed a temperature probe under the water heater insulation, against the tank. The display was inside his coach. He would let the water come up to (his) temp- say, 110 degrees- and then throw the switch to stop heating the water. Then he'd take his shower, using just the hot water. He boondocked, mostly, so he took "Navy" showers. Saved a lot of water that way.

Unhappily, the moment the shower starts the temp of the water in the tank starts to drop, as the cold water begins to replace the hot water drawn out. Under this process, the heat sources (gas and electric) will not come on. If you don't use much hot water, this is not a problem. If you do, well...

I should think a bona-fide temperature-control valve in the shower would allow you to keep the factory thermostats on the water heater and reduce the chance of scalding. The one I'd like to buy (link here) is expensive. And, it does not install on the "standard" four-inch centers. It does look pretty, though. I have seen look-alikes available for less money.
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Old 02-10-2020, 11:13 AM   #33
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I should think a bona-fide temperature-control valve in the shower would allow you to keep the factory thermostats on the water heater and reduce the chance of scalding. The one I'd like to buy (link here) is expensive. And, it does not install on the "standard" four-inch centers. It does look pretty, though. I have seen look-alikes available for less money.
Yes, an at the shower device could work for most people, but that would still leave the sinks and outside shower. Might not be the best for people with small kids.
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Old 02-11-2020, 01:51 AM   #34
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If my RV shower valve were to fail... then I would look into upgrading it to a Temperature Control Valve like this one you can buy on Amazon for $40:

https://www.amazon.com/dp/B082M73L38...NsaWNrPXRydWU=

Just know, these type of valves work best when when there is high pressure. So you need to make sure you can operate it in an RV with just the PSI output of your pump. But other than that, this type of valve will do a good job regulating the temperature, by mixing hot with cold water inside that little valve, and it should be an upgrade to what you have in your RV now... so long as you can get an escutcheons to cover the hole in the fiberglass wall.

Back to the subject of check-valves: When these thing work, there are no problems. However, they fail often. Specifically, when the top check-valve fails (the hot water... out side of the tank) then you might not be able to take a warm shower. And if the bottom-cold-water side check-valve fails open then you probably will not notice any hot water problems.


As for the physics of how a RV hot water tank works, you can either accept or reject what I have shared with you, but I base those claims on my personal experiences and what I learned first hand repairing my hot water tank.

...And in the RV world, isn't nice when you can fix a problem for zero cost? That's why I went to the extra effort to explain why you do NOT need check-valves (top or bottom) for your hot water heater to work; and that you are better off without them! So if they fail, "Drill them out!" ...aka "Gut the sucker!"
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Old 02-11-2020, 05:55 AM   #35
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Just a quick summary...

If a cold water inlet check valve exists, it is there to prevent a pressure rise in the cold water piping when the heater heats the water. If one removes (or modifies) the cold water inlet check valve, one should expect a pressure rise.

If a hot water outlet check valve exists, it is there to prevent filling the water heater tank with antifreeze when winterizing. If one removes (or modifies) the hot water inlet check valve, one should expect the hot water heater tank to fill with antifreeze- unless one installs or modifies the water heater bypass to account for the no-longer-there outlet check valve.
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Old 02-11-2020, 09:12 AM   #36
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Just a quick summary...

If a cold water inlet check valve exists, it is there to prevent a pressure rise in the cold water piping when the heater heats the water. If one removes (or modifies) the cold water inlet check valve, one should expect a pressure rise.
I really doubt it's there to prevent a pressure rise on the cold side. If pressure was the concern that would make the situation worse for the rest of the system because the expansion would be to only part of the system. The check valve would more likely be more to prevent hot water from entering the cold side.

Also flow would be better without the check valve. Pressure would vary depending on flow and the restriction of the check valve.
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Old 02-11-2020, 09:19 AM   #37
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Unless someone has a Shurflo expansion tank on their RV, and it was incorrectly installed on a hot water line rather than on the cold water outlet line near the water pump where it's supposed to be, hot water is not going to back flow into the cold water side of the RV.

If someone is getting hot or warm water out a cold water outlet in the RV, chances are they are not closing the hot and cold shutoff valves on a outdoor shower, rather shut off the water at the shower head, leaving hot and cold connected there.
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Old 02-11-2020, 09:24 AM   #38
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The easy way to prevent the temp/pressure relief valve on a RV hot water heater from operating when water expands due to heating is to provide additional expansion capacity to the RV using a inexpensive SHURflo expansion tank. It also makes the water system work much better when drawing water at low flow rates when dry camping.

That said if as said earlier in this thread you restore the air space in the top of the hot water heater tank that is enough expansion space to keep a properly working RV hot water system's from operating the temp/pressure relief valve.
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Old 02-11-2020, 09:38 AM   #39
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If someone is getting hot or warm water out a cold water outlet in the RV, chances are they are not closing the hot and cold shutoff valves on a outdoor shower, rather shut off the water at the shower head, leaving hot and cold connected there.
The other option would be a winterization bypass valve left open, possibly only partially.
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