Hot water pressure relief valve dripping - water not draining out of compartment

I don't know what that area is called so I am calling it a compartment.  The element needs to be replaced on our water heater and has to be ordered.  So for a few days we have it on propane instead of electric.  It is hotter on propane than it was on electric, and maybe that's because the element has been failing for awhile.  But the pressure relief valve is dripping when the heater is on and the water is pooling at the bottom of the compartment.  After every hot water heating, I have to go out and put a towel in the bottom of the compartment to soak up all the water.  Shouldn't that have a drain?  Our last TT dripped too, but I don't remember the water collecting at the bottom of the compartment.

Also, the hot water is scalding now.  Is there any way to adjust the temperature?

Can you tell us the brand and model of the water heater, the 2 most popular brands are Atwood and Suburban.  My first guess is you need  a new 12V control thermostat for the water heater that it is letting the water get too hot and the pressure relief is doing its job, though it too may need replacement.

You may have lost the "air bubble" at the top of the heater tank that allows for expansion as the water heats up. Over time, the air is absorbed by the water. Simply draining and refilling the tank will re-establish bubble. Installing an accumulator tank on the cold side will also manage the expansion issue for you, as well as cutting down on pump cycling.

Greycat,  I “use” the pressure relief valve” to eliminate the air bubble from the heater when filling. Sometimes, particularly if the unit was used in an area with poor water ( excessive minerals), hard water deposits can cause the valve “not” to seat properly! I’ve had this a few times.... I tap (gently) the “stem”, “seating” the valve and stopping the drip!


  Update:  This discussion starting me to think about the “air bubble”! There is varying opinions....bubble or no bubble? Both Atwood and Suburban, give info on how to regain the “bubble”. It appears that the “bubble” is recommended, though I’ve never had an issue with having a “full” tank!

There are some misconceptions here:

First, there should be no need to special order a heater element for your Rv system - it is a standard 1400 watt, 120v element and usually available wherever plumbing supplies are sold, including Depot, Lowes and many local hardware stores.

Second, a heater element rarely suffers a partial failure, i.e. loses some of its heat capability. It either works or burns out. If your heater works at all on electric, the element is fine.

Third, the water doesn't get hotter on gas than electric. It may get hot faster, but the final temperature is controlled by a thermostat, not by the type of heater. Since 2003, all Atwood water heaters use a single thermostat for gas & electric mode, so the temperature will be identical. Suburban heaters use a separate thermostat for electric and gas, but the temperature is the same for each.

The PT valve can drip a little for a variety of reasons, but the most common one is what NY Dutch described.  There should not be enough leakage to have water accumulate - ithe small amount evaporates almost instantly. If you have visible water, the leak must be more than a drip.

As far as the leak, standing to one side, open the relief valve and let it snap shut. That may reseat it. The water should drain out and not puddle up. No need to wipe it out. It should evaporate.

Gary, my suggestion above was that a single failed or out of range thermostat on a Suburban water heater could allow the water to be hotter on propane than on electric.

I had a similar issue with my Suburban water heater where if I left it on too long on electric mode, it would trip  the 12V propane thermostat safety cut off.

If should also be noted that there are adjustable aftermarket thermostats for the Atwood water heaters.

First, there should be no need to special order a heater element for your Rv system - it is a standard 1400 watt, 120v element and usually available wherever plumbing supplies are sold, including Depot, Lowes and many local hardware stores.
Where we live, there is no hardware store, just a small lumber yard and they don't carry many plumbing supplies.  It's easier to order an element than drive to a city to buy one.

Second, a heater element rarely suffers a partial failure, i.e. loses some of its heat capability. It either works or burns out. If your heater works at all on electric, the element is fine.
I don't know what to tell you there.  For the last week, I had noticed that the hot water in the shower wasn't lasting as long as usual, and Friday night it didn't last until the end of my shower, and that's a Navy shower.  When dh went in later to take a shower, the water was only luke warm from the start and then turned to cold.  That's when we switched over to propane.

Third, the water doesn't get hotter on gas than electric. It may get hot faster, but the final temperature is controlled by a thermostat, not by the type of heater. Since 2003, all Atwood water heaters use a single thermostat for gas & electric mode, so the temperature will be identical. Suburban heaters use a separate thermostat for electric and gas, but the temperature is the same for each.
There again, it may be that the element had been failing for awhile.  On electric, I could hold my hands under the hot water.  On propane, the hot water felt like boiling water.

The PT valve can drip a little for a variety of reasons, but the most common one is what NY Dutch described.  There should not be enough leakage to have water accumulate - ithe small amount evaporates almost instantly. If you have visible water, the leak must be more than a drip.
I don't know what else to call it.  It's a steady drip when the water is being heated.  Not just one drip that evaporates before it hits the bottom.  It's a drip that hits bottom and another separate drip on it's way down.  It's not a constant stream of water, just a constant drip.

Rene T said:

As far as the leak, standing to one side, open the relief valve and let it snap shut. That may reseat it. The water should drain out and not puddle up. No need to wipe it out. It should evaporate.

Click to expand...

My husband did that today, and put an elbow on the valve so it will drip into a bucket instead of inside the compartment.

Memtb said:

...
  Update:  This discussion starting me to think about the ?air bubble?! There is varying opinions....bubble or no bubble? Both Atwood and Suburban, give info on how to regain the ?bubble?. It appears that the ?bubble? is recommended, though I?ve never had an issue with having a ?full? tank!

Click to expand...

If you have an accumulator tank installed in the RV, the air bubble is not necessary. Otherwise, the bubble reduces the tank capacity by only a small amount as the air compresses under pressure. I've never measured one, so I don't know if there's an allowance for the bubble included in the stated capacity.

I replaced my PRV 2 years ago and it's still dripping while heating.

My pop off valve leaks quite often, but the water is so hot and the insulation so good, that we turn it on in the morning, then shut it off. It stays hot all day. In the evening for doing dishes or if we need more hot water during the day it takes about 15 minutes to become annoyingly too hot.

It is a 2010  Atwood gas/electric and the thermostat is fixed at the manufacturer.

When the valve does drip,  it collects in the bottom of the heater and drips over the edge to the ground.

Annoying but part of our RV life. 

Graycat said:

My husband did that today, and put an elbow on the valve so it will drip into a bucket instead of inside the compartment.

Click to expand...

When you say compartment, are you talking about the small space behind the door?  Snapping the valve shut, did the leak stop?

Here is what I know...and I have fixed many of these problems for friends and neighbor people at campgrounds.

The air at the top of the water heater tank is there by design.  It is there to allow for expansion of the heating water.  Air compresses and water doesn't.  When the water is cold and you heat it there will be expansion.  If there is air at the top of the tank it will compress.  If there is no air at the top of the tank the expanding water will push the relief valve open a little and it will drip water.  The fix for this dripping is to drain the tank, say halfway or so and refill it.  The design of the plumbing inside the tank will leave the air at the top of the tank as the tank fills.  The air will then be reestablished at the top of the tank as designed.  If your air has disappeared from the top of the tank that would indicate to me that you have not drained your tank in a long time.  I would take that opportunity to drain it completely and flush out the mineral deposits using a flush wand that attaches to the end of a water hose and is available at RV dealers, RV stores and most Walmarts.   

Very hot water "gushing" out of the relief valve is an indication of a different problem.  The water temp. in modern RV water heaters is controlled by a small thermostat, about as big as a thick dime with two wires attached.  If that thermostat fails there is also an emergency cut-off (ECO).  This is basically just another thermostat factory set at a higher temperature.  During normal operation the thermostat is controlling.  If the thermostat fails the water heats up until the ECO acts as the thermostat and shuts the heating off.  The ECO is then controlling...acting as the thermostat.  If you stay in your RV a lot you may notice the hotter than normal water.  That would indicate a failed thermostat and the ECO controlling at the higher temp.  Time to change the thermostat and the ECO...they are sold together as a kit and easy to install.  Just follow the instructions in the kit.

If you do not notice the hotter than normal water temp. the ECO will continue to act as a thermostat until it fails.  When the ECO fails the water will continue to heat up until the relief valve opens, due to high temperature or pressure and very hot water gushes out of the relief valve.

In conclusion:  A dripping of water out of the relief valve is an indication of a loss of the air that is suppose to be at the top of the hot water tank.  A gushing out of hot steamy water out of the relief valve is an indication that both the thermostat and the ECO have failed. 

Here is a question, when I fill my 6 gal. hot water heater and turn on the hot water tap, the air trapper inside rushed out blowing mist and spray all over the sink. So, I keep the hot water tap open until the tank fills.

That would mean the only air left in the hot water tank is the few inches of space between the outlet pipe and the top of the tank. Is that air cushion you are referring to?  ??? 

Graycat, you still have not told us which brand of water heater you own, the model would also be nice to know.

For example if you have a Suburban brand of water heater they have separate thermostat for the electric element and the propane controller.  A failing electric control thermostat could cause lower water temperature when on electric, so the electric heating element may be fine, and you would still have hotter water on propane as it is controlled by a different thermostat.

If you have an Attwood water heater this may not be the case as they use the same thermostat for both propane and electric.

RGP said:

Here is a question, when I fill my 6 gal. hot water heater and turn on the hot water tap, the air trapper inside rushed out blowing mist and spray all over the sink. So, I keep the hot water tap open until the tank fills.

That would mean the only air left in the hot water tank is the few inches of space between the outlet pipe and the top of the tank. Is that air cushion you are referring to?  ??? 

Click to expand...

Yes... That air space is sufficient for the expansion when heating.

RGP

When you fill your water heater you have to let the air that is pushed out of the tank by the water go somewhere.  If you don't it will compress and make some big spits and splashes when you open a faucet.  The compressed air may also prevent your water heater from filling to it's proper level.  Most manufactures call for opening the Pressure and temperature valve (P&T valve) to let that air out while the tank is filling.  Since the P&T valve is located below the top of the tank this will not eliminate the air gap at the top of the tank.  The hot water outlet is also located below the top of the tank to allow the air gap to be established as the tank is fills.  It may not "appear" that these outlets are below the top of the tank.  In that case the actual outlets are established internally via pipes so that the designed air gap is established.

Some manufactures call for opening a hot water faucet, preferably the closest faucet to the water heater.  I use that procedure.  If there is water in the RV system it will be pushes out the faucet by the air.  Do not mistake that for a full water heater!  That water flow will be followed by a spitting of air and water...mostly air.  When the water heater is full (less the designed internal air gap) and only water flows out of the faucet let it run for a time until all air is removed and there is no spitting.  I like to run all the water outlets...faucets, showers, toilet, etc. after the water heater is full to eliminate any trapped air so there are no spitting/splashing surprises when I use the water on a trip.

If we were trying to troubleshoot a malfunction such as the water will not heat, burner won't stay lit or won't light, etc. I would need to know the brand and model of your water heater.  For replacement parts you often need to know the serial number also.  For this problem of dripping out of the P&T valve and for filling the water heater no brand is needed.

Here is a question, when I fill my 6 gal. hot water heater and turn on the hot water tap, the air trapper inside rushed out blowing mist and spray all over the sink. So, I keep the hot water tap open until the tank fills.

That would mean the only air left in the hot water tank is the few inches of space between the outlet pipe and the top of the tank. Is that air cushion you are referring to?

Click to expand...

You don't need to worry about too much air escaping when the faucet spits and sputters - it is self-adjusting.  The outlet pipe is located near the top of the normal water level but below the top of the tank, so that there will still be an air cushion above it.  Each of the hot water faucets will have some air that will get vented during the first few uses.

Atwood included these air gap instructions in their heater owner manuals. It is intended for an occasional check/replenish of the air gap, but it also works for an initial fill if you leave the water supply on at Step #2.  Opening the PT valve releases the water until it is below the level of the valve and thus there is air & steam at the PT rather than hot water. That is usually enough to eliminate seepage.

TO REPLACE THE AIR GAP FOLLOW THESE STEPS:
STEP 1: Turn off water heater.
STEP 2: Turn off incoming water supply.
STEP 3 Open a hot water faucet in coach.
STEP 4: Pull handle of pressure-temperature relief valve
straight out and allow water to flow until it stops.
STEP 5: Allow pressure-temperature relief valve to snap shut; close hot
water faucet; turn on water supply.

Click to expand...

If you lose the air pocket at the top of the water heater's tank between tank flushing, an easy way to replenish it is to drain your fresh water hose, i.e. make it full of air.  Connect the air filled hose between the shore water spigot and the RV and turn on the shore water.

Now go inside the RV and turn on a HOT water spigot.  The air in the hose will be drawn into the hot water tank and replenish the air pocket.  If you get a little sputtering at the faucet, it's confirmation the air pocket is full and the excess air in the hose is flowing to the faucet.

There's no reason to open the overpressure valve by hand, as has been noted this can lead to leakage if debris gets caught in the valve.

So why does an RV hot water heater need an air pocket, but a stick house water heater doesn't?  Water expands when it's heated, in a stick house it just pushes back and displaces some of the incoming cold water.  That's why home water heaters specify there must be a minimum distance between the last branch in the incoming cold water line and the inlet to the heater's tank.

An RV's water system is a closed system, with one way check valves at the water pump and at the city water inlet.  Unless you have an accumulator tank, or the air bubble in the water heater tank, there's nowhere for the water to go when it expands, so the pressure rises until something gives and relieves the excess pressure.

If you're lucky, this will be the overpressure valve on the hot water tank.