Sudden onset of dripping from pressure relief valve pipe

[ghatfuswow]

We've owned this water heater for around 9 or so years and I've never seen anything come out this pipe before. Now every 8 hours I end up catching 3-6 cups of water.

The valve may need replacement, but I'm just trying to see if it may be something else before I try to swap it out.

 

[Jadnashua]

It's probably doing its job!

That valve opens if the pressure gets to 150-psi, or if the temperature gets to 210-degrees F. The more common problem is pressure. You likely have a closed water system meaning that there's either a check valve or a PRV that acts like one in your home and an expansion tank. If so, the expansion tank is likely shot, and needs to be replaced. If so, it will typically sound with a thunk if you tap on it, and if you momentarily open the Schrader valve (they type you'd have on a tire) on the bottom, it will probably leak water.

When heating water, it expands...copper pipe (well most types) won't expand much at all when that happens, and if there's no place for it to go, the pressure will spike when the water heater runs when there isn't an open valve or someplace for it to leak. That's what an expansion tank is for.

At about 9-years, you're on borrowed time on most water heaters. It could last for years, but may be having issues, and excessive pressure can make those happen faster.

 

[Sponsor]

 

[ghatfuswow]

It's probably doing its job!

That valve opens if the pressure gets to 150-psi, or if the temperature gets to 210-degrees F. The more common problem is pressure. You likely have a closed water system meaning that there's either a check valve or a PRV that acts like one in your home and an expansion tank. If so, the expansion tank is likely shot, and needs to be replaced. If so, it will typically sound with a thunk if you tap on it, and if you momentarily open the Schrader valve (they type you'd have on a tire) on the bottom, it will probably leak water.

When heating water, it expands...copper pipe (well most types) won't expand much at all when that happens, and if there's no place for it to go, the pressure will spike when the water heater runs when there isn't an open valve or someplace for it to leak. That's what an expansion tank is for.

At about 9-years, you're on borrowed time on most water heaters. It could last for years, but may be having issues, and excessive pressure can make those happen faster.

My home is older with iron piping and doesn't seem to have an expansion tank.

About the only thing I can figure now is maybe the temperature got set too high on the heater and it's only just now doing this.

Could there then be an internal problem causing this?

 

[wwhitney]

If you put a pressure gauge with a max reading needle on a nearby hose bib or laundry supply or the drain valve of the water heater, you can tell if the pressure is spiking, causing the pressure relieve valve to activate as it should, or if for some reason it is misbehaving.

If the pressure is spiking, you need an expansion tank. As to why the behavior just started, it could be that you fixed a constant leak somewhere (which could have been relieving the pressure), or the city changed their water meter to a new style that includes a check valve, or a variety of reasons.

Cheers, Wayne

 

[ghatfuswow]

I got a pressure gauge and tried it at the water heater drain and it gave me a reading of around 90 PSI. I also got a water temp of 150F so it seems neither pressure or heat are an issue.

I then kind of wiggled the pressure valve closed and open a few times and I noticed the dripping became a lot less. I suppose the relief valve might be sticking or something, so I guess it may be bad after all.

 

[Reach4]

I got a pressure gauge and tried it at the water heater drain and it gave me a reading of around 90 PSI. I also got a water temp of 150F so it seems neither pressure or heat are an issue.

I then kind of wiggled the pressure valve closed and open a few times and I noticed the dripping became a lot less. I suppose the relief valve might be sticking or something, so I guess it may be bad after all.

There is a good chance that the pressure would show much higher after you use a lot of hot water, and then stop using water.

Yes, replace that T&P valve. But also put in a thermal expansion tank, or alternatively put in a pressure relief valve, about 130, to keep the pressure from ever getting high enough to trip the T&P safety valve.

There are two things you test for with the lever: does the valve open, and does it close.

 

[ghatfuswow]

There is a good chance that the pressure would show much higher after you use a lot of hot water, and then stop using water.

Yes, replace that T&P valve. But also put in a thermal expansion tank, or alternatively put in a pressure relief valve, about 130, to keep the pressure from ever getting high enough to trip the T&P safety valve.

There are two things you test for with the lever: does the valve open, and does it close.

After reading your post I got curious. I ran the shower for ~10 minutes and then after I turned it off, I watched the pressure gauge and relief valve drain pipe.

After about 25 minutes, it did start dripping quite profusely. I noticed there was no change on the pressure reading and the temp of the water coming out was 125F.

 

[Reach4]

After about 25 minutes, it did start dripping quite profusely. I noticed there was no change on the pressure reading and the temp of the water coming out was 125F.

That seems odd if you monitored the gauge the whole time. If the pressure gauge reading did not change, I would think this is a stuck gauge.

If the gauge rose, and then returned to a lower reading after the dripping started, that would be normal. How about taking a movie of the gauge Including the 25 minutes after you turn the shower off.

 

[Jadnashua]

Where I live, to pass a plumbing inspection, you must have an expansion tank. Their reasoning is that (eventually), all of their customers must be operating with a check valve per federal regulations to prevent any back-siphoning into the main distribution system and potentially contaminating the public water supply. That can happen if the pressure drops, like when a lot of fire hydrants are opened, or some other hiccup...left your garden hose in a puddle? Could get dog poop, fertilizer, and who knows what sucked back into the water supply (which is also why they call for vacuum breakers on hose bibs, but not everyone has them, especially older houses).

SO, the point being...the utility could have added a check valve in normal system maintenance without you knowing, and now you have a closed system, and that would mandate an expansion tank to avoid this sort of problem.

The T&P valve is a safety device, and if it is operated on a regular basis, could fail when actually required. This is a safety issue, as well as a practical problem. FWIW, 90-psi is too high, residential water pressure by code should be 80-psi or less, so if what you're seeing isn't related to thermal expansion, you should have a pressure reduction valve installed in addition to the expansion tank that might be hidden somewhere and has failed. Normally, they're easy to find, but it could be tucked behind something and you didn't notice it, or high up in the ceiling.