Water heater venting - why?

I have an auxiliary water heater, 110V electric, in a master bedroom that's about 50 feet from the "hot water core" of the house. It's worked perfectly for nearly two years, but now has started venting regularly from the popoff valve. (Which made a mess, initially, as I hadn't bothered to install a proper drainoff line...)
I've fixed and tried everything and it's still occurring; anyone who has a clue as to why is most cordially invited to share a clue with me. :)
1) It's a 2.5 gallon 110V electric that feeds only the sink. 2) It was recently reinstalled with tidier plumbing in a remodel - the first round was kind of hacked and slashed into the existing cabinet. 3) Both the cold tap and the heater pull from the cold water line; the existing hot supply line is capped. 4) It worked perfectly for a year before, and for a couple of months after the remodel. 5) The temp was set moderately, about 125. I've tried cycling the temp setting back and forth to free any stickiness and set it down to 110. 6) I flushed the blowoff valve several times. 7) I emptied some hard water scale and grit from it while replacing the blowoff valve. 8) I finally switched the fraggin' thing off for a couple of days.
It continues to vent, about a cup at a time, several times a day. It's apparently unrelated to the heating function, since it's still doing it with the power off. I can't match the blowoff to any other event in the house (showers, other water use, etc.) And the main heater isn't doing it.
Either I got a bad valve with the new one, or there's some sort of surge in the lines exceeding the 150 psi blowoff point. Or...?
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|=- James Gifford = FIX SPAMTRAP TO REPLY -=|
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Id try yet another new Relief Valve (popoff valve) . Providing your thermostat/element is working correctly, if a new Relief Valve doesnt do the trick, id get rid of the water heater. You can get a 2.5 gallon Water Heater for $119 in Home DePot.
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snipped-for-privacy@webtv.net (JustCallMe Norman) wrote:

I can't see any flaw in the heater itself that would be causing this - it's 100% the popoff valve, and the only thing the heater could be doing is overheating - which it can't, with the power off. I've never encountered overtemp water, either, so I don't think that's happening.
Someone elsewhere suggested that it might be water hammer, exaggerated by the long piping run, causing brief overpressure. I'm going to do the drain- the-house thing to empty the hammer shock absorbers and see.
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Is there a "shock absorber" (first time I've seen it called that) near the sink? A 50' run's an awful long ways to not have one there. But, since it did work and doesn't now, you're probably on the right track unless that valve is just no good.
Pop
James Gifford wrote:

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(JustCallMe Norman) wrote:

This is Turtle.
Invest $6.00 in a new pop valve and see.
TURTLE
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James Gifford wrote:

My suggestions are likely a bad valve. Other possibilities include an increase in water pressure supplied to the heater, or a pressure build up in your system when the water is heated. You may need an expansion tank. If you have anti-water hammer devices they may work as expansion tanks until they fill with water and maybe draining them may help.
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Joseph Meehan

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That would be two of them - strange. I could hunt down a better-quality one than HD gar-bahz, maybe.

If turning the heater off had stopped the problem, I would have had an avenue to work on - overheating, excessive expansion, etc. But it does it with the power off and the tank ice-cold. Strange!

Draining the lines to clear the hammer-stoppers is the next step - haven't done it for several years. I just really hate putting up with all the sputtery, hissing faucets afterward. :)
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James Gifford wrote:

It's the valve, period! Ok, the first valve went bad. The second valve may also been bad or you may be the problem. I think your original statement gave a clue, "I flushed the blowoff valve several times." Buy a new valve and leave it alone. DO NOT operate the valve after you install it, and if you are of the persuasion to test it (foolish in my opinion), then you need to operate (reseat) the valve under zero water pressure conditions (that is turn off the cold water, open a hot water tap, wait until their is only a drip coming out, and then operate the t/p valve. If you feel the need to test the t/p valve (operate as part of safety tests for some other purpose) you would be better off removing the valve and replacing with a new valve. This is a constant subject in RV groups which find that t/p valves may not seat correctly under pressure. You may get away with sometimes, but you won't get away with it all the time.
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<snip> If you feel

If the TO&UP valve won't seat under pressure, it is not functioning properly and might not work if needed. I have always found the dribbling valve after a test problem to be cured by letting a little water flow out the valve open fully before letting it spring back to do the trick.
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Roger Shoaf wrote:

First, dribbling is "not functioning properly" but likely no indication that the valve won't pop open under high temp or pressure. In fact, a case could be made that a dribbling valve is more likely to pop open since it is already partially open.
Your experience on dribbling valves is by no means universal.
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On Fri, 31 Dec 2004 23:01:06 -0000, James Gifford

You need to find out what your water pressure is at or near that device. If the pressure is indeed exceeding the 150psi then you need an expansion tank. Your local city may have recently installed a backflow preventer on your water line. Of course the likely hood of a 2nd bad relief valve is there but I doubt it. Then again, maybe that undersink water heater is just a piece of chit! Bubba
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Bubba wrote:

and pressure regulator.

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Is there another water heater in the plumbing system also?
In my neck of the woods houses have a backflow preventer out in the water line from the street.
When I opened any faucet in the house the water would surge out in a burst then quickly subside to normal flow & I realized that the water hoses for the clothes washer were acting as an expansion tank and swelling up quite a bit as the pressure rose due to the cold water expanding as it was heated, so I added an expansion tank .
Bert
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On Sat, 01 Jan 2005 02:08:51 GMT, "Joseph Meehan"

Nope! Check the pressure with all faucets closed. Water heater burner or heating element not on. If pressure is managable, then turn the water heater burner or electric elements on. Now watch the water pressure. IF it starts rising, you most likely have a backflow preventer in the line and you will need an expansion tank. The pressure regulator on the incoming line to the house is just to control the amount of pressure you want to your home, usually because the pressure provided by the city is too high. Bubba

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IOW, its probly the other water heater that's causing the ( closed ) system to over pressurize.
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Bubba wrote:

...
I think we are both right, and I hope we can agree and therefore give the best possible advice.
You are right if the 150 lbs of pressure is a result of a backflow valve and a water heater. That may well be true and I would expect it to be the most likely issue.
However if there is not backflow valve or there is one and it is not the water heater but rather the street pressure that is over 150 lbs, then a pressure regulator is needed or the one there replaced.
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