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Open Roads Forum  >  Tech Issues

 > Water Heater Pressure Relief Valve Leaking?

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Conch Cruiser

Southport, North Carolina

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Posted: 02/12/09 07:20am Link  |  Print  |  Notify Moderator

My pressure relief valve leaks from time to time. Is it more likely that the relief valve is going bad (’96 model) or is the water heater over heating? The water does not seem to be too hot at the tap.

Is it common for a pressure relief valve to go bad?


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NORM WADDELL

PENSACOLA FL 32514

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Posted: 02/12/09 07:26am Link  |  Print  |  Notify Moderator

This is not a problem
The tank is FULL (no
air at the top) and
when the water is heated,
it expands...it HAS to
go somewhere, so it
goes out the relief valve.
You can open the relief
and open a hot water faucet
(with no water pressure on
tank) and allow air to get
into tank.....or,just don't
worry about it.


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bldrbuck

one or the other

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Posted: 02/12/09 07:49am Link  |  Print  |  Notify Moderator

While I agree the relief valve may open occasionally and appear to leak it may also be caused by the type of water you are using. Hard water can cause deposits that can not be removed and cause a contineous leak. If that occurs the valve must be replaced. This is an easy task on a home water heater. It can be a real pain on an RV water heater. I just replaced mine and it was a real chore. The thing was 19 years old and totally corroded. It is near impossible to get a good grip on it since the manufacturer of the valve did not provide an surface to get anything but a pipe wrench on. Due to location that did not work. The valve is basically back in a hole and a good square grip is impossible. Mine was cut into pieces using a Dremal tool and cutoff wheels. it came out in many pieces. I would take it to an RV shop next time. Good luck.


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Rollincool

RI

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Posted: 02/12/09 07:52am Link  |  Print  |  Notify Moderator

Conch Cruiser wrote:



Is it common for a pressure relief valve to go bad?


Absolutely it is.

Campgrounds with hard water, opening and closing it everytime you drain the tank, age. They go bad. When they do, they start dripping.
Very easy to replace. Just make sure you get the correct replacement.

Conch Cruiser

Southport, North Carolina

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Posted: 02/12/09 08:17am Link  |  Print  |  Notify Moderator

thanks for the input, I will continue to monitor and replace if it gets worse.

Washboy

Denver, CO

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Posted: 02/12/09 09:18am Link  |  Print  |  Notify Moderator

From Watts "Water Safety and Flow Control"
When water is heated it expands. For example, water heated from 90ºF to a thermostat setting of 140ºF in a 40 gallon hot water heater will expand by almost one-half gallon. This is because when water is heated, its density decreases and its volume expands. Since water is not compressible, the extra volume created by expansion must go someplace. During no-flow periods in a system, pressure reducing valves, backflow preventers, and other one-way valves are closed, thus eliminating a path for expanded water to flow back to the system supply. Hence, system pressure increases.

Thermal expansion of water in a closed plumbing system can create a number of annoying and potentially dangerous problems. These include: the build up of unusually high pressure in a system (even when a pressure reducing valve is installed); pressure surges; and the chronic or continuous dripping of a temperature and pressure (T&P) relief valve.

More serious problems can also occur due to thermal expansion. When dangerous pressures are built up in a water heater, internal parts may fail such as the internal flues, fittings or water connections. If a flue way collapses it can lead to the potential release of toxic gases, such as carbon monoxide into living spaces. Thermal expansion can also lead to a ruptured or distorted hot water heating tank and may void the manufacturer’s warranty.

Plumbing codes require that thermal expansion control be addressed in plumbing systems. A temperature and pressure relief valve is not considered a thermal expansion device. This is because when water is allowed to continuously drip from the T&P relief valve, minerals from the water can build up on the valve, eventually blocking it. This blockage can render the T&P valve useless and potentially lead to hot water heater explosions. The International Plumbing Code (IPC), Uniform Plumbing Code (UPC) and Standard Plumbing Code all require thermal expansion control.



My thoughts and opinion:
The RV water heater is designed to operate without a thermal expansion device but only if it is filled and operated properly. An examination of the RV water heater will reveal the design differences from a residential water heater. Residential heaters are fitted with their inlet and outlet ports at the top of the tank. An RV water heater’s inlet and outlet ports are located on the side of the tank…below the top and above the bottom. This design allows a properly filled system to retain a small “bubble” of air at the top of the tank, effectively creating an expansion area inside the tank. The lower port, located above the bottom of the tank provides a “sediment settling” area to reduce passage of mineral solids into the plumbing supply piping.

Proper filling of the RV water heater will almost always result in the expansion air bubble forming automatically. But, over time and with continuous connection to a pressurized water source, this expansion air bubble will diminish, resulting in a “waterlogged” water heater…no air bubble to absorb the expansion.

Many RV owners discover their water heater’s T&P dripping shortly after connecting their plumbing system to a hydrant with excessive water pressure, overlooking the recommendation that a water pressure reducing valve be installed in the system. Or, they discover the T&P valve leaking after several hours of non-use of the water system…i.e. overnight…even with their inexpensive RV water pressure regulator installed. This is due to the inexpensive regulator allowing the system pressure to equalize on both sides of the regulator. But, many times, the cause of the T&P valve’s leakage is due to improper filling of the RV’s water system.

Improper filling is easily accomplished by the uninitiated RV owner. They connect their supply hose to the RV and hydrant, open the hydrant’s valve and immediately enter the RV to open the faucets to expel the air from the piping. Should this procedure include opening a hot water faucet before the water heater is completely filled, the air bubble at the top of the water heater tank will not form, being expelled along with all the air in the piping.

To properly fill the system, one should allow the newly connected water supply to stop flowing before opening any faucet inside the RV. Once the water system is pressurized and non-flowing, slowly open all of the COLD water faucets to expel the air. Then, slowly open the hot water faucet furthest from the water heater until the air is purged from the piping. Repeat the hot water valve opening for the remaining fixtures until all the fixtures flow without spitting air. The water heater should now have it’s air bubble properly formed at the top of the tank and the system is ready for use.

As stated earlier, long term connection and usage of the water supply will eventually diminish the water heater’s air bubble. The solution to this issue is to simply re-establish the bubble.
(1) Turn off the water supply
(2) Open the RV’s hot water low point drain and a hot water faucet for several minutes.
(3) Close the drain and faucet and slowly reopen the water source.
(4) Slowly open the hot water faucet until the air is expelled from the piping. The air bubble inside the tank should now be re-established.

For full timers, a long term solution to this issue is to install a small thermal expansion tank into the cold water supply plumbing. The expansion tank will completely eliminate the need to maintain the water heater’s air bubble.


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heavyputer

Ontario, Canada

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Posted: 02/12/09 09:37am Link  |  Print  |  Notify Moderator

What "Washboy" said..........It's true....and no amount of flushing or popping of the PRV will change that. Replacing the air pocket is the correct fix. Very seldom is a new PRV required. JMHO


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Conch Cruiser

Southport, North Carolina

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Posted: 02/12/09 10:22am Link  |  Print  |  Notify Moderator

Thanks, for the additional info. I will look into that idea.

Corkey05

Washington State

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Posted: 02/12/09 10:45am Link  |  Print  |  Notify Moderator

Adding an accumulator tank to the water system solves the problem of air absorption. You'll never have to burp the hot water tank again.


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