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Old 01-13-2020, 03:52 PM   #1
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Hot water heater overflow valve

I recall seeing something earlier but canít remember where. My WH overflow is leaking - as if the pressure was too high. Just a little dribbling but still dribbling.
I think I saw somewhere that this is ok and that thereís a quick fix.
I think I saw that you just empty the WH and refill?
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Old 01-13-2020, 03:58 PM   #2
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Sometimes if not all the time when we turn on our HWH—as it comes up to temp, pressure will build—and it will start to dribble down the outside of the coach just a little bit. It's not big deal.

We just go into the kitchen and turn on the not water faucet for about 5 second to relieve the pressure and it's all good from there.
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Old 01-13-2020, 08:03 PM   #3
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Check water temps, might be a bad thermostat 140* and working off the high temp limit 180*.
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Old 01-14-2020, 04:54 AM   #4
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CWP3-

Here is the "quick fix" you remember seeing.

You don't say whether you have an Atwood or Suburban water heater.

Atwood manual:
Quote:
Dripping Pressure Temperature Relief Valve

Weeping or dripping of a pressure-temperature relief valve while the water
heater is running DOES NOT mean it is defective. This is normal expansion of
water as it is heated in the closed water system of a recreation vehicle. The
Atwood water heater tank is designed with an internal air gap at the tank to
reduce the possibility of weeping and dripping. In time, the expanding water
will absorb this air. To replace the air follow these steps:

1. Turn off water heater.
2. Turn off incoming water supply.
3. Open the closest hot water faucet in the coach.
4. Pull handle of pressure-temperature relief valve straight out and allow
water to flow until it stops.
5. Allow pressure-temperature relief valve to snap shut, close the faucet
then turn on the water supply.
Suburban manual:
Quote:
Seeping/Dripping

If the pressure relief valve on the back of the water heater seeps or drips water, you may have lost the air pocket that is normally present at the top of the water heater. This can occur over time.To re-establish the air pocket, follow these steps:

1. Shut off the water heater (LP and electric)
2. If using city water, turn off the faucet. If on internal water, turn off the pump.
3. Open a hot water faucet in the RV.
4.Carefully open the pressure relief valve and allow water to flow out until it stops flowing.
5. Let the pressure relieve valve snap back to the closed position.
6. Close the hot water faucet and turn on the water supply.
7. Turn the water heater on and check for normal operation.

If the seeping/dripping continues, the pressure relieve valve is probably defective.
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Old 01-14-2020, 07:15 AM   #5
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Thank you. Thatís the info that I recall seeing. Now if only I could remember that the next time the WH dribbles!
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Old 01-14-2020, 09:30 AM   #6
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Every RV water is supposed to have an air pocket in the top of the tank, this is for cushioning the effect of expanding water when heated. The relief valve operates by over-pressure and over-temperature.
Shut off water supply, then relieve pressure. Remove the heater drain plug and open relief valve for a few seconds, allow relief valve to snap shut, replace drain plug, turn on water supply. Unless the relief valve seat and seal are dirty or damaged you should have no more leakage.
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Old 01-14-2020, 10:40 AM   #7
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I had it once leaking I just went to HD and got a new valve.
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Old 01-14-2020, 08:26 PM   #8
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I see you recently joined the forum. If it is a new rig, look to the former answers. If it is an old rig, it could be hard water deposits, and the last suggestion might be the solution.
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Old 01-14-2020, 08:59 PM   #9
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I ran the hot water for a while and it hasnít leaked since.
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Old 01-16-2020, 08:15 PM   #10
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The last RV I had sometimes dripped. I would just snap the relief valve open and shut and it always stopped dripping.
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Old 01-16-2020, 09:48 PM   #11
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Quote:
Originally Posted by 00 Buckshot View Post
The last RV I had sometimes dripped. I would just snap the relief valve open and shut and it always stopped dripping.
That is logical, relieved pressure. Would not happen if the air pocket is present.
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Old 01-17-2020, 03:43 AM   #12
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Stupid question:

Has anyone ever seen an RV water heater relief release because of pressure?

It strikes me that this thing is plumbed in through some awfully insubstantial-looking plastic tubing, and that if the water system ever got anywhere near pressurized enough to pop off the water heater relief valve, the tubing would have let go or swelled up long before that point.

Or am I just underestimating my plastic tubing?
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Old 01-17-2020, 05:09 AM   #13
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The typical RV P&T valve is rated 150 psi and 210 degrees Fahrenheit.

When a P&T (pressure and temperature) relief valve "weeps," there are two likely causes:

1) pressure has reached 150 psi, or
2) The valve seat has some crud on it

Logic says if the P&T valve opens due to pressure, then that pressure will be felt throughout the water system, unless there are check valves to prevent it doing so.

I have confirmed this. I have put a gauge on the water system for troubleshooting. Without the air pocket, pressures in the system reached just under 150 psi, at which time the relief valve began to weep. Leaks did not occur anywhere else in the water system at that time, despite the high pressure. How many 150 psi cycles the water system could withstand, I do not know.

If the water heater has an inlet check valve (and it is working correctly), the cold water system pressure will be what it is at the cold water inlet to the RV, even if the hot water system pressure reaches 150 psi.

Two takeaways:

1) The water system piping and fittings are more robust than most realize, and
2) Maintaining the air pocket in the water heater reduces the chances of a pressure-induced leak in the hot water system and, if an water heater inlet check valve is not present or not working, in the cold water system, too.

On our coach, I was unable to maintain an air pocket in the water heater for any length of time. So, I had to take other measures to prevent a constant high-pressure condition. Except for the few folks like me, the wise advice is to re-establish the air pocket in the water heater as soon as the P&T valve shows signs of weeping.
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Old 01-17-2020, 05:28 AM   #14
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"1) The water system piping and fittings are more robust than most realize,"

That must be the key, then. Thanks. My plastic lines just look . . . weak, but I guess they're stronger than I thought. I was toying with the idea that the relief valve was unneeded - like an alarm that goes off when I lift 800 pounds with my left arm.

Did you just mount an expansion air tank on the system to keep a compressible air bubble? That would be my impulse.
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