Water heater pressure relief valve leaking. Advice needed

davenApril 19, 2014

Recently purchased a condo that has a gas water heater with power vent. I discovered a rubber hose connected to the pressure relief valve downspout and there has been water leaking from the valve.

What is the probable cause of this and what is required to fix this? I have never seen this happen in any other water heater.


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The valve you are talking about is a pressure relief valve (PRV). It is a safety device to prevent WH explosions.

Either the valve is bad and needs to be replaced with EXACTLY the same spec valve despite what a vest wearing know it all at a box store says... "this one fits everything".

Or you have a closed plumbing system and you have a thermal expansion problem that needs to be corrected NOW.

If you have a closed plumbing system, and that has been code since the 90's, there should be a small thermal expansion tank installed proximate to the WH. These tanks have a bladder that may have failed and the tank must be replaced.

OR... you have a closed plumbing system and there is no thermal expansion device installed, which is not uncommon, and there needs to be one installed. In this case the PRV is acting as a thermal expansion device and it is NOT intended to.

Here's some light reading on thermal expansion... http://www.watts.com/pages/learnabout/thermalExpansion.asp

If this seems beyond your skill level call a plumber... and do it SOON.

    Bookmark   April 19, 2014 at 12:53PM
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Very common for sediment to get under the valve and cause leakage. Lifting the valve manually can cause the seat to clear, however it is also possible to scald oneself or have a major blowdown if the valve does not shut.

Some people manually lift the relief annually to prevent this very thing.

The thermal relief is required whether or not you have an expansion tank.

    Bookmark   April 19, 2014 at 5:30PM
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The heater is off so I will try lifting the valve tomorrow.

    Bookmark   April 19, 2014 at 6:25PM
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PRV valves are not designed for intermittent use. Whether the cause of the leak is dirt or excess pressure is irrelevant. For sediment to get under the valve (in the valve seat, the valve had to be opening and that is indicative of a bad valve or excess pressure in the plumbing system. The valve should be replaced and the cause of the valve failure identified and repaired.

Thermal expansion is one of the most ignored and misunderstood plumbing conditions by both homeowner and handyman(woman) types. Thermal expansion problems are common and easy to resolve.

    Bookmark   April 19, 2014 at 7:33PM
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Er, ah, OK... as I said, "Some people manually lift the relief annually to prevent this very thing." Note the words 'annually' and 'prevent.'

Additional, by design of this valve and its significant "blowdown" it is not dripping a few drops to prevent an overpressure situation due to a solid system.

This post was edited by saltidawg on Sat, Apr 19, 14 at 20:13

    Bookmark   April 19, 2014 at 8:10PM
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Hey Dave,

As mentioned before, the expansion tank (or lack thereof) may be the source of your problem, as Lurker has mentioned. You will want to resolve that problem if you have it.

In any case, replace the valve. It's just not worth dinking with it.

But something that wasn't said - the hose on the outlet pipe really isn't kosher.

The pipe coming from the PRV must not be reduced in size from the outlet of the PRV (or have any kind of valve on it). It should terminate near a drain and it must be visible if there is a water discharge.

    Bookmark   April 20, 2014 at 10:00AM
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I just had a customer who's newly installed hot water heater began to leak after 3 months. (Turned out the Installer kept the existing expansion tank when he installed the new tank.). PRV was dripping about 1/2 gallon/day. New expansion remedied it. (Work done by a pro.)

    Bookmark   April 21, 2014 at 10:16AM
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what was the final determination?


    Bookmark   April 23, 2014 at 12:14PM
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