Water Heater over pressurizing system? Exploding Water Filter Housing

[wurlitzer28]

I tried to post this in the Water Heater section but, according to that section, I'm not allowed to post. What the????

Not a freezing issue but on a 60F day with only my onboard water pump running.

This 35' Georgetown had been used after the winter on both RV park and internal water pump operation so the water filter housing was at that time OK. No water related issues after the anti-freeze was replaced with potable water.

We set up and turned on the water pump and the water heater. About 15-20 minutes later a loud bang and water was pouring out of the side of the RV's water compartment.

The best I can figure, is when water is heated it expands and if there is no place for it to go, the pressure will rise very rapidly and very high as water does not compress.

What is in the RV to prevent water pressure from rising when the water heater is turned on? If there is no way to relieve pressure these water filter housings should be going off like popcorn so something must be in the system to try and keep this pressure increase under control.

[KyDan]

Your rig has pex water lines which can expand a bit. I do not think it was water heater related. The slight water expansion would not be enough to do it IMO. Water filter housings break fairly often according to what folks report here. Unless your water heater stuck on AND it's pressure relief valve stuck shut which is a really long shot. This is why I use a whole house filter on the outside of my trailer.

[Retired JSO]

Did the Pressure relief valve malfunction?

[wurlitzer28]

Originally Posted by Retired JSO

Did the Pressure relief valve malfunction?

No idea other than the bang was quite loud indicating quite a bit of pressure.

[Retired JSO]

You can manually release pressure to test by lifting the tab.

[wurlitzer28]

Originally Posted by KyDan

Your rig has pex water lines which can expand a bit. I do not think it was water heater related. The slight water expansion would not be enough to do it IMO. Water filter housings break fairly often according to what folks report here. Unless your water heater stuck on AND it's pressure relief valve stuck shut which is a really long shot. This is why I use a whole house filter on the outside of my trailer.

Thank you for responding.

The temperature differential in an RV vs a home system where the water is only heated to 125 or so degrees would IMO be significant. The RV water heater is set higher thus always requiring a mix of cold water to keep your skin intact.

I had not entertained the idea that the pex water lines could absorb some of the pressure change but you are probably right as they are not ridged.

Re and outside vs inside water filter {in the water compartment under the rig. I would prefer, not like, but prefer the filter housing break rather than a water line somewhere in an inaccessible wall. Does your external Whole House filter still function with the RV's internal pump.

What I am gathering is there is no separate expansion tank like I have in my home for both my hot water furnace and hot water tank.

[nomad297]

I can’t tell you how many times I have brought this up here.

Your water heater will easily cause the pressure of your water system to reach 150psi on both the hot and cold sides. Once it reaches 150psi, the temperature and pressure relief valve on the water heater will slowly dribble water until the pressure is just below 150psi. Your RV’s water system is a closed system, so the pressure caused by thermal expansion has nowhere to go until you either turn a faucet on, the T&P relief valve relieves the excess pressure, or something breaks — like a cheap water filter housing or a bad PEX crimp.

Some people will claim there is a magic pocket of air at the top of your water heater that will absorb this excess pressure, but, even if there was, it isn’t enough to compensate for the expansion created by heating a completely cold tank of water up to 120-140 degrees. And if you do lift the lever on the T&P relief valve, there goes that magic air pocket at the top of the tank since the T&P relief valve is at the top of the tank.

This is all I have to contribute to this thread because I know how this one always goes.

Bruce

[pgandw]

In a very small plumbing system like in our A-frame, the pressure increase can be significant.

I found after trailering in the warm sun all day, the pressure in the water system was above pump pressure, and the pump would not come on until I released pressure. I would also find the fold down galley spigot leaking a little water on to stuff stored in the sink from a combination of pressure and vibration of the valve.

Due to the above, started releasing pressure before trailering - and that has solved all the problems. I turn off the water pump AND open the outside shower valves - both hot and cold. When the dribbling stops, close the valves and leave the pump off. We are good to go. Arrive at destination, turn on the water pump, and pressure is restored very quickly.

Fred W
2019 Flagstaff T21TBHW A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time

[Mr. Dan]

Originally Posted by wurlitzer28

I tried to post this in the Water Heater section but, according to that section, I'm not allowed to post. What the????

No one can post anything in any subcategory of the forum’s Frequently Asked Questions (FAQ). It is not a member input section of the forum. The thread is now in the correct sub-forum.

[TowPro]

I am betting it was a problem with water filter housing weak.

All the rvs made through the years why don't this happen all the time?

[TitanMike]

I'm thinking the same thing. Housing could have a flaw or possibly damaged earlier by being dropped or possibly overtightened.

Sometimes looking at all the pieces will reveal where it failed and msybe reveal a possible cause.

I read earlier that RV water systems are tested wd ith air pressure over 100 PSI. Would be interesting to know the max design pressure for the filter housing. Usually far higher than just the wd orking water pressure.

[TowPro]

But.

After a shower tonight the pressure valve was dripping on HW heater. I opened a faucet and there was no blast of high pressure. Tomorrow i will let some air into HW tank to see if it stops dripping while heating.

I was going to remove filter under bed in future. Might be a good place for a small expansion tank.

[wmtire]

Originally Posted by nomad297

I can’t tell you how many times I have brought this up here.

Your water heater will easily cause the pressure of your water system to reach 150psi on both the hot and cold sides. Once it reaches 150psi, the temperature and pressure relief valve on the water heater will slowly dribble water until the pressure is just below 150psi. Your RV’s water system is a closed system, so the pressure caused by thermal expansion has nowhere to go until you either turn a faucet on, the T&P relief valve relieves the excess pressure, or something breaks — like a cheap water filter housing or a bad PEX crimp.

Some people will claim there is a magic pocket of air at the top of your water heater that will absorb this excess pressure, but, even if there was, it isn’t enough to compensate for the expansion created by heating a completely cold tank of water up to 120-140 degrees. And if you do lift the lever on the T&P relief valve, there goes that magic air pocket at the top of the tank since the T&P relief valve is at the top of the tank.

This is all I have to contribute to this thread because I know how this one always goes.

Bruce

On the Suburban tank type water heaters the T&P is "near" the top but not at the very top. This allows for an air pocket above the level of the T&P valve.

In our FAQ section, we have 5 video guides provided by Suburban. One of those videos is about the temperature and pressure valve which explains with diagrams the expansion space at the top of the tank and how to replenish, how much expansion is required for water temps, and using an add-on expansion tank if necessary.

https://www.forestriverforums.com/fo...es-135977.html

Hope it helps everyone.

[joshuajim]

Originally Posted by nomad297

Some people will claim there is a magic pocket of air at the top of your water heater that will absorb this excess pressure, but, even if there was, it isn’t enough to compensate for the expansion created by heating a completely cold tank of water up to 120-140 degrees. Bruce

Do the science. The amount of expansion of water in the range you mentioned is about 2%. I guarantee you that the manufacturer calculated the amount of “magic” air needed for expansion in their design.

[KyDan]

According to Google water expands about 4% when heated from room temp to boiling.
Since our WH is only heating to about 135 deg we might guess that will mean 2% expansion.
More than I'd thought.
That's about a pint if you are talking about 6 gallon water heater.
I'm gonna guess there's more than a pint of air in the top of a WH due to the round shape of the tank and the outlet pipe comes out the side rather than the top.
I suppose the expansion is a factor but in my 4 trailers and 15 years of camping we've never had a problem.
I'm not gonna start worrying about it now!

[NMWildcat]

Originally Posted by KyDan

According to Google water expands about 4% when heated from room temp to boiling.
Since our WH is only heating to about 135 deg we might guess that will mean 2% expansion.
More than I'd thought.
That's about a pint if you are talking about 6 gallon water heater.
I'm gonna guess there's more than a pint of air in the top of a WH due to the round shape of the tank and the outlet pipe comes out the side rather than the top.
I suppose the expansion is a factor but in my 4 trailers and 15 years of camping we've never had a problem.
I'm not gonna start worrying about it now!

X2. Never even heard about anyone in an RV having problems due to heated water expansion. I'll add it to the long list of things that OTHER people worry about......
I'll let my SIL know about this so she can have another RV area to agonize over and drive my BIL nuts..... I owe him one

[wurlitzer28]

The filter/housing was OEM from FR {as far as I can tell} Fr1 Water pur KW1} And now longer available. The new housing is RCS. Very similar to the original but they must have made a change for some reason. #1 cost????, #2 a failure rate higher than could be covered up with normal sales BS.

RE: The approx 2% expansion. Depending on the system, rigidity of the plumbing, air pockets, a 2% volume increase could be minimal or greatly exceeding the PSI ratings pushing it to failure as water is NOT compressable..

[wurlitzer28]

Originally Posted by Mr. Dan

No one can post anything in any subcategory of the forum’s Frequently Asked Questions (FAQ). It is not a member input section of the forum. The thread is now in the correct sub-forum.

The snarky "Search is your Friend" is what took me originally to the section where I could NOT post.

[SailorSam20500]

Originally Posted by wurlitzer28

Re and outside vs inside water filter {in the water compartment under the rig. I would prefer, not like, but prefer the filter housing break rather than a water line somewhere in an inaccessible wall. Does your external Whole House filter still function with the RV's internal pump.

What I am gathering is there is no separate expansion tank like I have in my home for both my hot water furnace and hot water tank.

That you are using your water pump, that implies you are putting water into your FW tank. I use my external filter setup as I fill the tank. FWIW, I never directly hook to city water. All water goes into the FW tank.


I installed a 2 gallon expansion tank. Keeps the pump from cycling every time we use water. Good for keeping the pump silent over night.

[TitanMike]

Originally Posted by SailorSam20500

I installed a 2 gallon expansion tank. Keeps the pump from cycling every time we use water. Good for keeping the pump silent over night.

I found that turning my pump off at night worked really well for that task.