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Old 02-11-2020, 03:37 PM   #1
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Water heater over-presurized?

Hi, everyone! I ran into an issue with my water heater on my 2020 Flying Cloud 27FB this weekend and I’m trying to determine what caused the issue so that I can avoid the issue going forward.

I came home to the Airstream to find water dripping from the outside water heater access panel. There was noticeable steam coming from the panel as well. When I opened the panel, hot water was spraying out of the tank from the drain plug. Not from the threads, but from the actual plug head. It seems that the tank was so pressurized that water began forcing its way out of a crack that developed in the drain plug head.

To troubleshoot, I turned off the city water source and ran the water pump and fresh water tank. The pump sounded much different than I remember, but I’ve only used the pump once or twice. The pump was much louder than before and sounded something like a machine gun. I turned the pump off and drained the water from the faucet until the water in the lines ran dry. This stopped the water from spraying out of the drain plug. But any time I would run the water pump, or turn on the city water, the water heater tank would almost immediately pressurize and begin spraying water from the drain plug again.

I thought it might be as simple as a failed drain plug, so I allowed everything to cool and drained the hot water tank and replaced the plug. So far, everything seems to be okay now. But I’m concerned about how much pressure built up in the tank that it would cause the plug to fail. I replaced the OEM plug about a month ago with the cheap Camco drain plugs from a local RV store.

Can anyone recommend what I might check to avoid this potential over-pressure issue in the future? My wife did admit to running the water pump while hooked up to flowing city water. I’m pretty sure that when she did, the fresh water tank was completely empty. But it somehow allowed water to enter the fresh water tank because it is now 40% full. I read in the manual that it’s okay to run the pump on city water to help with lack of city water pressure - but with the fresh tank being dry... maybe it added an excess of air to the water heater tank?

Any thoughts or recommendations? We’re full-timers and I do leave the water heater on, electric, most of the time. Didn’t think that would be an issue but maybe worth mentioning. Thanks!
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Old 02-11-2020, 03:55 PM   #2
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Water heater over-presurized?

Jasper

I found a simple pressure gauge at Lowe’s in the plumbing dept attaches directly to a water spigot. That can at least give you a quick psi check. Them maybe a regulator to knock down psi if required.

But shouldn’t the T&P safety release any excessive system pressure by discharging it. Like it should.

Did you just have a bad drain plug and it just failed?

Gary
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Old 02-11-2020, 05:04 PM   #3
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I think that this is a case of a bad plug or the plug was not completely tightened into the tank. If you were to get too high a pressure in the tank, it would be released from the pressure release valve. As this did not happen, I don't think you had too much pressure in your HW tank. As the water heater heats the water, it expands, which builds up pressure in what is now essentially a closed system. When the pressure builds up enough, the T&P relief valve on the water heater just does it's job and relieves the excess pressure by leaking a little water. I believe that will happen when the temps reach somewhere around 210 degrees or the pressure reaches about 150 lbs.

A good practice when removing or replacing the drain plug is to use several wraps of teflon tape on the plug threads before putting it in and make sure it is good and tight.
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Old 02-11-2020, 06:44 PM   #4
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When I took deliver my of my ‘19 Globetrotter, I had an issue with the water heater where it wouldn’t stop heating. The thermostat in the water heater was bad.

Some of this sounds similar to your issue, but if replacing the plug worked, then maybe not. If I left the water heater on it would just keep heating. Eventually the water would boil over and would first leak out the bottom of the trailer and then spew out the side of the trailer. Better than than blow up, I guess. Apparently it was a quick fix.

For that first shakedown trip I basically just turned the WH on until the water was hot then shut it off. Could leave it on during showers because the water was being exchanged. Wasn’t a huge deal for a few days.
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Old 02-11-2020, 07:40 PM   #5
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I completely agree with the warden, your problem is completely exclusive to the drain plug which either had a manufacturing flaw or was otherwise damaged after the fact. Most likely was a plastics cooling/shrinkage flaw that developed into a crack and failed early after several expansion/contraction cylces which caused the crack to propagate. The pressure safety valve 100% prevents over pressure. The plastic plug is rated far greater than the safety valve set point.

You replaced the failed part, don't spend any more energy worrying about excessive pressure. To elaborate further the safety valve is there to prevent the tank from bursting in the unlikely event someone closes the inlet and outlet valves while it is cool and then turns it on or it gets stuck on. With either the inlet or outlet valve open, a plastic pipe fitting will come loose and release water at a controlled rate before the tank or mechanically sound plug fails.
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Old 02-11-2020, 08:01 PM   #6
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I agree that the drain valve was the failing component here. There is a pressure relief valve in te water heater to prevent over pressure situations. I sounds like that valve never opened.

Running the water pump with an empty tank should not increase the tank pressure as the pump will shut off when the output pressure reached a reasonable level, somewhere around 45 psi.

Water entering the fresh water tank while on city water is usually a problem with the check valve that is built into the water pump which is leaking and allows water to pass through the pump and into the tank. Pumping water will often reset the valve and eliminate the problem.

I am surprised that you would travel with no water in the tank.
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Old 02-11-2020, 08:21 PM   #7
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I should have talked a bit about the pump as Richard did. Running the pump dry or nearly so for a short time won't damage it as it would take some time for it to overheat, and since air is compressible and water is not, air in your piping system provides a cushion against over pressure. It sounded like a machine gun because it still had air in the lines which increases the pulsating effects of the pump. So don't worry about the pump either. Richard provided great advice about the check valve and you finding water in your clean tank.
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Old 02-11-2020, 09:12 PM   #8
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One of the first...

...thing's we did, get rid of the plastic plug.

POI...we always use the FW pump and fill the tank as needed, eliminates over pressure worry.🤓

Bob
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Old 02-12-2020, 04:07 AM   #9
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Another side note, Our AS’s have a water pressure regulator installed behind the city water hookup with issues arising regarding RV installed equipment such as this water regulator I found that for piece of mind I install another external pressure regulator at the spigot as well, just to be safe, also it might be wise to turn off your water heater as well as the city water feed when leaving for any period of time one never knows what might happen to a late Friday connected water line under the kitchen cabinet, Just Sayun!
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Old 02-12-2020, 05:41 AM   #10
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The relief valve should have blown before the plug failed. I expect you got a cheap PVC plug and it melted from heat. Did the tank freeze recently? The original plastic plug is made from tough Nylon. Also if any plastic plug is over tightened it can strip or split. The water heaters get very hot. I have measure temps up to 145 degrees. They do this to make the water last longer but it can melt some things that are not made for it.



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Old 02-12-2020, 06:03 AM   #11
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In this scenario, the observation "...replaced the OEM plug about a month ago with the cheap Camco drain plugs..." looks like more of a cause-and-effect than coincidence.

If the OE plug was not bad, my vote is to find it, give it a few wraps of Teflon tape, and replace the cheap thing.

Rhetorical question is why the OE plug was replaced as there was no notation of an issue with it.

As already noted, the trailer should have a pressure regulator at the city water connection. Using a separate stand-alone pressure regulator between the city water spigot and far end of the hose is a good practice as it reduces stress on the hose. Having two pressure regulators inline with each will not hurt anything.
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Old 02-12-2020, 06:48 AM   #12
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^
On another side note...not all the AS gizmo's are all that reliable.
Our water pump lasted pretty well, replaced last Season.
We usually run our water heater for 2hrs in the morning. In Summer it's usually good for the rest of the day, it's only 6gal 1/2hr=pretty hot.
The water pump is only on during the day and NEVER when sleeping or away.

Bob
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Or under the Bathroom sink...on our first trip, cross threaded/cracked.
Thank goodness for MarineTex, 17yrs SFSG.(great addition to your kit BTW) 👍
Also sooper, along with toothpicks in the hole, for fixing stripped wood screws on all those cabinets that keep falling off the walls.

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Old 02-12-2020, 07:51 AM   #13
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There's only two ways excess pressure gets into the WH.
1. High city water pressure. But the Airstream has a water pressure regulator in the line, no?
2. The WH is boiling the water and steam is building just like in a locomotive. You mentioned steam. This needs attention because water that hot is not safe to shower with, the pressure may blow out a line, and draining the tank is dangerous.
Make sure the WH control board is not boiling the water.
If it is, then replacing the plug to contain the pressure is just causing the steam to find another way to escape, like a ruptured water line.

BTW, my water heater has been very reliable, and I still turn it off after I shower. It stays hot enough for dishes a long time. No reason to tempt fate.
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Old 02-12-2020, 08:08 AM   #14
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I had to replace the thermostats in my Atwood water heater last year. The high temp was not shutting the unit off, and the water temp was almost boiling. The pressure relief valve did not open, as the pressure did not rise enough to cause it to function. I suspect that is the problem with the OP's water heater. The original drain plug, made of nylon, will withstand much more than the "cheap" Camco plastic replacement. Reinstall an original nylon, or get the brass plug with the integral drain valve. A test of the water temperature leaving the taps will confirm if the unit thermostats need to be replaced. It's not a big job!!
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Old 02-12-2020, 08:45 AM   #15
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I had nearly the same thing happen to me last summer. I was sitting outside and noticed a drip coming from the water heater. I checked and saw it was coming from the plug. Since I had just replaced the Teflon tape on the plug I figured I'd just give it a little turn. BOOM! No shower needed today, I just got one. The plug blew, leaving the threads inside. Those plastic things are hollow. I replaced the plug (another story in itself) and haven't had any problems since. You had a bad plug from the start, should be OK now.
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Old 02-12-2020, 08:54 AM   #16
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X2= snip...[] "The WH is boiling the water and steam is building just like in a locomotive.[]"

If your WH is BOILING water, Houston... You have a problem. 😡

Bob
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Old 02-12-2020, 09:02 AM   #17
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Those “cheap” Camco replacement plugs are made of nylon, identical and probably made in the same factory as you original plug. That of course does not preclude the possibility of getting a bad one. Replacing it with another, and if no further problems, you should be fine. If the heater keeps blowing plugs, it’s time to look at you thermostat, pressure relief valve, etc.

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Old 02-12-2020, 02:28 PM   #18
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The plastic plugs are not intended to be removed and replaced on a regular basis, doing so fatigues the threads and the plug will fail prematurely. Hopefully most of you have a separate drain valve. If not and you must use the plug to drain your tank, consider a replacement with an integral drain valve next time you remove it.
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Old 02-12-2020, 03:17 PM   #19
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I've had my plug crack and start leaking on my trailer also. Apparently it is a common issue and may not be indicative of an over pressurization problem. I went to the closest RV dealer to my home rather than go to my local dealer. I'm assuming that Nylon plugs are used for cost purposes and maybe to keep from having dissimilar metals causing corrosion between the tank and the plug.

The parts guy at the SOB dealer said it is a fairly common failure and he had carries nylon plugs there. He recommended that I buy two so I always have a spare on hand in case the replacement plug fails in the future. Considering I've had my trailer for 17 years now, and replaced one plug, I don't think we have any issues here. I only pull the plug once a year when I winterize and scour the tank.

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Old 02-12-2020, 04:05 PM   #20
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The plugs are not failing due to over pressure, it is a physical impossibility due to limits of the connected systems. The threaded plugs are rated for 300Psi while the tank itself is rated for 150psi (200 de-rated to 150) and has a 150psi safety relief valve to protect it against catastrophic burst. The city inlet has a 65psi regulator and while city water components weakest point have ratings of 200psi, pressure rarely exceeds 100psi. The water tank is capable of causing over pressure which is why the safety valve is located there. The water pump can cause over pressure but has a built in pressure safety valve. The water tubing has a max working pressure of 160 psi. So the safety valve in the tank in effect is protecting the entire system so long as valves remain open.

There is no cause to continue to speculate about an over pressure issue.
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