Captain, She'll blow for sure!

[jimmoore13]

Interesting experience today.
Factory faucet inlet hose blew off the faucet on the hot water side. Hot water was on, and, I presume, the heated water generated higher pressure than the 60 PSI spec on the factory faucet. The hose popped off the barb fitting on the base of the faucet. What passes for a clamp on the connector hose could not cope with the pressure.

How high can the pressure get on the output side of the hot water heater?

I'm now the proud owner of a new kitchen faucet, built to home standards with soldered copper connections. Will install tomorrow. Here's hoping Scotty doesn't make the same prediction about the warp drive in my new faucet.

PS. I made a pit stop to dump tanks and perform this repair. About to leave again, so I won't be responsive to replies until early next week. Eager to hear about hot water pressure.

[craigav]

I thought that the pressure would be the same on the hot and cold side... but maybe not according to the link below. Are you using a pressure regulator?

Here is a link I found to read further.

https://inspectapedia.com/plumbing/H..._Expansion.php

~CA

[jimmoore13]

Originally Posted by craigav

I thought that the pressure would be the same on the hot and cold side... but maybe not according to the link below. Are you using a pressure regulator?

Here is a link I found to read further.

https://inspectapedia.com/plumbing/H..._Expansion.php

~CA

We are boondocking...using the water pump. On the rare occasions that we use hookups, I do use a pressure regulator.

Thanks for the hunch on output pressure on the hot water tank. That makes sense, but I know that as temps rise, so may pressures.

[Old and soft]

Shouldn't the blow off valve on the water heater vent first?

[ARoamer]

Originally Posted by Old and soft

Shouldn't the blow off valve on the water heater vent first?

Not at 60 PSI, the water heater T&P valves are much higher. Check the tag on it. "Factory preset to 150 psi and 210 degrees Fahrenheight"
The temp I get, but pressure is kind of a joke as a RV can't even stand 60 PSI...

I'd guess a bad crimp on the PEX tubing let it go. I noticed some fittings start to drip on my 5er over 50# of pressure. I never go over 45#

[Onyrlef]

Originally Posted by jimmoore13

Interesting experience today.
Factory faucet inlet hose blew off the faucet on the hot water side. Hot water was on, and, I presume, the heated water generated higher pressure than the 60 PSI spec on the factory faucet. The hose popped off the barb fitting on the base of the faucet. What passes for a clamp on the connector hose could not cope with the pressure.

How high can the pressure get on the output side of the hot water heater?

I'm now the proud owner of a new kitchen faucet, built to home standards with soldered copper connections. Will install tomorrow. Here's hoping Scotty doesn't make the same prediction about the warp drive in my new faucet.

PS. I made a pit stop to dump tanks and perform this repair. About to leave again, so I won't be responsive to replies until early next week. Eager to hear about hot water pressure.

Definitely, most likely, probably, maybe, as Aroamer said, a bad crimp. Matter of fact if the fitting is properly crimped the fixture or the pipe itself will fail before the crimp connection. Not true however for sharkbite fittings, where the connection is the weak point or in the old butyl pipe with both the aluminum and/or copper crimp where the butyl fitting itself was the weak point. Dammit Jim, don't succumb to temptation and use a shark bite on the new faucet unless you're sure to keep the pressure regulated always. Incredibly some local residential codes even allow sharkbite connections insides the walls.

[curver900]

not sure this could cause high water pressure, if hot water heater that had air in it, heating up the water with a bunch of air could be possible. I doubt it though. As others said bad crimp and/or just cheap faucet that failed sadly they are just the cheapest faucets you can get with a bid for the cheapest faucet

In order to get pressures to blow parts apart and or the safety valve on your hot water heater the thermostat would probably have to fail and boil the water .

[GTS225]

Yep.....bad crimp, and added thermal expansion from the hot water heating up the hose and "clamp".
Just a minor incident, that you were lucky enough to be there when it happened, or the collateral damage could have been bad.

Roger

[jimmoore13]

Prepping to roll out soon, but I agree that it was a cheap factory faucet. Oddly, the faucet itself seems to be chrome-plated brass. It's quite heavy. But the connection pigtails were the weak link in the chain...all parts plastic. The new faucet I bought to replace it has soldered copper input lines with brass connectors soldered on. I imagine Jayco saved $1.50/fixture, so there you go.

For any following for tips and tricks, so far, the consensus on two different forums is that the pressure created by heating the water (pressurized by the onboard pump from the fresh tank) would, at minimum, be balanced between hot and cold. Most believe the pressure would NOT rise significantly. That's a bad assumption.

My own crude analysis...
a) pump pressurizes the lines feeding cold water and the hot water tank...up to, perhaps, 55 PSI...maybe on a good day.
b) check valve in pump prevents bleeding that pressure back into the fresh tank.
c) with all faucets closed, we now have a closed, sealed system.
d) hot water heater raises temperature/pressure in hot water tank, AND both the hot water output lines AND the cold water side...which simply tee's off the output side of the freshwater pump.
e) during hot water use, the pressure is relieved, BUT the hot water tank fires again to restore temp in the tank...AND, WHEN DONE USING THE HOT WATER, the tank continues to fire until it reaches the thermostatically-controlled temp and shuts off.
f) again, this is a closed, sealed system with heat being added to cooler water, so one assumes the pressure will rise as temp rises. But the thermostat shuts off the flame well before pressures rise enough to trip the blow-off valve. (Water heating never even causes mine to "weep.")
g) so my assumption is that water pressure may rise considerably as the water heater raises the temp.

As it turns out, the water pressure DOES rise a lot as the water is heated.
https://inspectapedia.com/plumbing/H...ure%20increase.

So, I guess the moral of the story is, TURN OFF YOUR WATER PUMP and/or shut off your city water input (perhaps using a 1/4-turn ball valve on the end of the potable water hose) whenever you are away from your rig, AND turn off the water heater if you don't plan to use it for a while. For extra measure, if on city water, once you turn off the water heater, open the hot water faucet for a moment to relieve the pressure. ESPECIALLY IF YOU ARE RUNNING FACTORY FAUCETS AND SO ON IN YOUR RIG. (When boondocking, water may be too precious to waste relieving pressure this way.)

Had we not been in the camper when the hose popped off the back of the faucet, our water pump would have happily pumped the entire contents of our fresh tank - perhaps 20 gallons at that moment - into the interior of our camper. As it was, it took us only about 30 seconds to recognize that the sound of the water pump meant something was very wrong, so we shut off the pump and soon saw water flowing out from under the kitchen sink cabinet. Two large bath towels soaked up the mess. The dry air of Colorado will take care of the rest. But in the humid Eastern states, we would have had to mitigate the moisture or face mold.

Hard lesson learned at little cost to us. But we've been camping with the pump on nonstop...or connected to city water...for more than a decade, and we've never experienced a failure like this.

[craigav]

I haven't heard of any problems like you described, however it makes sense and a lot of RV'rs here state they carry pex clamps and tools, perhaps they are not aware of why they need to make these repairs.

I believe my unit doesn't have a check valve at the water heater, I will check soon. I read that the older ones used more valves for winterizing and don't need a check valve.

My engineering thought would be to have a pressure relief valve installed in the hot water line at ~15 psi higher than your water inlet regulator is set to and have that pressure relief valve outlet plumbed into the line that fills that water holding tank to prevent any water loss (just drop the excess into the tank)... or like you stated, just keep the water heater off when not needed, or at least allow the pressure to escape as it comes up to temperature by opening one of the hot water valves during the heating.

Perhaps a pressure gauge on the water lines would also be helpful. I wouldn't mind having a lower temp on my water heater but I don't think there is a thermostat to adjust, which would be nice to have. ~CA

[jimmoore13]

I'm not a hydraulic engineer, but I have several observations.

More than one video (from authoritative sources) confirms that there is a substantial pressure increase, either to the hot water side only (check valve on hot water heater input) or to the entire water system.

Furthermore, the colder the input water supply (e.g. ground well water vs. city water vs. onboard fresh water tank) the greater the temperatue/pressure increase to achieve the thermostat shutoff temp. My failure came from the relatiely tepid water temps of my holding tank. How much more pressure rise would result from 55 degree well water?

WHY don't RV manufacturers include an "accumulator tank" to help absorb some of this pressure?

Why did Jayco, in this case, install a faucet that has a label on its input hoses warning to avoid any pressures above 60 PSI? Said faucet was also fed by the soft lines normally used on the water pump...NOT PEX.

Why do RV hot water heater manufacturers NOT include a temp adjustment on the thermostat...as home hot water heaters have?

What is the max pressure rating on my bathroom faucet, outside shower faucet, inside shower faucet, plastic PEX fittings, and the soft line exiting the water pump...and the check valve in the water pump and the pump itself?

The deeper into this thread we go, the more angry I get at the utterly despicable level of "engineering" that goes into such an important system in the rig.

One large-as-possible accumulator tank comin' right up, but this is inexcusible.

[jimmoore13]

Originally Posted by craigav

<<SNIP>>
My engineering thought would be to have a pressure relief valve installed in the hot water line at ~15 psi higher than your water inlet regulator is set to and have that pressure relief valve outlet plumbed into the line that fills that water holding tank to prevent any water loss (just drop the excess into the tank)... or like you stated, just keep the water heater off when not needed, or at least allow the pressure to escape as it comes up to temperature by opening one of the hot water valves during the heating. <<SNIP>>

Makes sense until you consider that, without a check valve on the input side of the hot water heater, the entire hot/cold water system is pressurized by the increased pressures in the hot water tank...all the way back to the water pump check valve and city water input check valve. In other words, there is NO WAY TO REGULATE the rig's internal water pressure increase from the hot water heater, other than have a large accumulator tank to absorb some of the pressure increase and, perhaps, turn down the water heater temp.
As I begin to understand what's happening, it's clear the RV manufacturers and the RV hot water heater manufacturers are perfectly willing to send out these rigs with water systems that are ticking timebombs.
See my follow-up post.

The ONLY upside is that, without a checkvalve on the input side of the water heater, the entire plumbing system helps equalize the pressure...slightly. Bear in mind that water itself DOES NOT COMPRESS. But all the fittings and lines can stretch slightly to absorb some of the pressure increase. Grrrrrr.

[craigav]

Originally Posted by jimmoore13

Makes sense until you consider that, without a check valve on the input side of the hot water heater, the entire hot/cold water system is pressurized by the increased pressures in the hot water tank...all the way back to the water pump check valve and city water input check valve. In other words, there is NO WAY TO REGULATE the rig's internal water pressure increase from the hot water heater, other than have a large accumulator tank to absorb some of the pressure increase and, perhaps, turn down the water heater temp.
As I begin to understand what's happening, it's clear the RV manufacturers and the RV hot water heater manufacturers are perfectly willing to send out these rigs with water systems that are ticking timebombs.
See my follow-up post.

The ONLY upside is that, without a checkvalve on the input side of the water heater, the entire plumbing system helps equalize the pressure...slightly. Bear in mind that water itself DOES NOT COMPRESS. But all the fittings and lines can stretch slightly to absorb some of the pressure increase. Grrrrrr.

Lots of thoughts for sure. I now suspect that many RV'rs who ask why their check valve failed, or one of the water lines leaked, or as you mentioned the entire line comes off the fitting, just consider that the reason must be something specific to the item that failed and not realize what really caused the issue.

With that in mind, I never had this problem with over ~8 different RV's I have owned, however during the past 35 years or so, I have noticed that years back I would test the water heater pressure relief valve and always had air come out for a few seconds before water did. What I suspect is that because I often drain the tank when not using the RV and rarely if ever do I open the relief valve anymore (for many years but on occasion) that there must be an air gap at the top of the water heater tank.

So... as a thought, I would suggest that draining the water heater tank prior to each adventure (or regularly, perhaps weekly) and then using the RV in a regular manner (not opening the relief valve while camping) that in doing it that way would keep an air gap at the top of the tank as long as the T&P relief valve holds. Just a thought. ~CA

[craigav]

Perhaps this could be part of the solution. I never knew they made these. IMO these should be standard equipment.

This along with an air gap at the top of the tank would alleviate a lot of the pressure concerns.

~CA

[craigav]

Or this non-adjustable but lower temp model. This one is 125~130, some of the reviews say that the original is 168f which I wouldn't doubt, my hot water gets scalding hot for sure. ~CA

https://www.amazon.com/Atwood-91470-...e%2C164&sr=1-4

[jimmoore13]

Thanks for the suggestions for temp mods and ensuring the air spring is captive in the hot water heater!!

[jimmoore13]

We're camping 4 days or more out of every 7...boondocking. The RV only comes home to be serviced once every two weeks. A long way of saying that I can't afford to dump 6 gallons of water per week...but I WILL dump when I come home for service...for sure.

Meanwhile, a bit of experimenting. As you might suspect, the extra pressure is relieved quite easily. When the water heater is running...just prior to use...I crack the cold water valve until the pump starts. Same when the hot water heater reaches temp and shuts off. I can run the cold water faucet for about 2 seconds or so before the pump starts. As soon as the pump starts, I close the valve. We're back to pump pressure levels. Less than 1/2 cup of water comes out under higher pressure before the pump starts.

As soon as the hot water heater reaches temp, we turn it off. There's plenty for dishes and/or shower...especially when boondocking and we're lakefront for "baths."

Accumulator tank on order. I may turn down the water temp, but we old folks don't have problems with scalding, and the higher temp means longer lasting hot water. I'll chew on that one.

Thanks all!!