Replaced T&P Valve... still leaking

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Old 11-23-19, 06:54 AM
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Question Replaced T&P Valve... still leaking

Hi,

My T&P valve was leaking, and I replace it with a brand new one seemingly without issue. A few hours later, it was leaking again.

What could be the most likely cause? Is it possible that I didn't put it on tightly enough? I've also read this could be the result of a faulty expansion tank.
 
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11-23-19, 07:54 AM
Pilot Dane
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If a new T&P valve is leaking through the valve I'd investigate why especially since you had leaking from the previous valve so something is causing it. They open up due to pressure and/or temperature. What is your water pressure? Do you have an expansion tank on your water heater? How hot is the water in your heater?
 
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Old 11-23-19, 07:03 AM
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Is it leaking at the threaded connection or through the spout? if leaking through at the threads did you use TFE tape or paste? If so you need to tighten it up a bit. If it leaks through the spout then perhaps there is some sediment that is getting stuck in the sealing surface. Allow a long and heavy spurt to flow out and clear the orifice.
 
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Old 11-23-19, 07:54 AM
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If a new T&P valve is leaking through the valve I'd investigate why especially since you had leaking from the previous valve so something is causing it. They open up due to pressure and/or temperature. What is your water pressure? Do you have an expansion tank on your water heater? How hot is the water in your heater?
 
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Old 11-23-19, 09:15 AM
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What is your water pressure?

I believe this is probably your problem. The water pressure is very likely to be increasing because of a faulty expansion tank, but you'll never know till you check the pressure.
 
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Old 11-30-19, 10:33 AM
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So I checked the pressure and it's hovering around 90/95, too high. Does that mean it most certainly have to do with the expansion tank or could it be something else?

The leak from the T&P valve is still happening when we run hot water, but it is much slower than before replaced the valve. Before it was a constant drip, and now it only happens when we run the water.

One other note: the temperature on the tank was set to high. I turned it all the way down to low, but it doesn't seem to have any impact on how much hot water we get.
 
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Old 11-30-19, 02:01 PM
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So I checked the pressure and it's hovering around 90/95, too high.

What is the normal water pressure? Do you have a pressure reducing valve? If normal pressure is around 50 to 60 psi and the 90-95 psi is after the water heater fires, you have a bad expansion tank.
 
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Old 11-30-19, 03:25 PM
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You need both a working pressure reducing valve (PRV) and expansion tank. They work together. The PRV limits the pressure of the water coming into your home. The pressure tank then gives the expanding water in your water heater somewhere to safely go.
 
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Old 12-02-19, 01:18 PM
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So the PRV valve is separate from the T&P valve? If so, I don't believe I have a PRV valve, but I know I have an expansion tank. Is that possible?
 
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Old 12-02-19, 02:51 PM
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A PRV, T&P and expansion tank are all separate items. All three are required in most areas now but the PRV is a new requirement in the past 15 years. Most homes older than about 15 years don't have a PRV.

The PRV is installed on the main water line to your home and is usually the first device so it can protect everything in the house. Often it's right where the water main emerges from the ground in the crawl space or where it first enters the basement.

You should check to make sure your expansion tank is not water logged. If it is completely full of water it offers no protection.
 
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Old 12-02-19, 06:49 PM
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The house was built in 1998 and I moved in a couple of years ago, so guessing it does not have a PRV valve. In any case, I don't see it where the water comes in.

So I'll need to have one installed? I'm wondering why there is a need now after 20 years. Is it possible that replacing the expansion tank will solve my problems without a need for a PRV?
 
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Old 12-03-19, 05:37 AM
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Yes, installing a PRV would be on my "to do" list. 90/95 water pressure is too high. I would get it down to about 60.

Have you checked to see if your expansion tank is waterlogged? If not then why replace it. You still need a PRV either way.
 
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Old 12-03-19, 05:57 AM
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Many houses built before 1998 had PRVs although I suppose it depends on your local city water pressure. I don't have one on my house but it's high above the meter and my nightly pressure spikes are only around 50 psi. PRVs are adjustable. I'd double check to make sure you don't have one.

I'm fairly ignorant about expansion tanks but my house along with all our sons don't have expansion tanks and have no issues. The kids all have PRVs installed shortly after the water line enters their crawlspaces.
 
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Old 12-03-19, 06:04 AM
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Every new tankful of water expands when heated. In the past there may have been some air pockets in the plumbing that got squashed and prevented the water heater relief valve from tripping.

Also, prior to the installation of a pressure regulator near where the main cold water pipe enters the house, the expansion may have pushed back into the water main so the pressure inside the house did not get so high.

You will need to get the expansion tank situation squared away.
 
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Old 12-03-19, 08:30 AM
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Long ago there were no check valves or back flow preventers. The house's plumbing was open to the municipal water system. When the water in your water heater expanded it could push out against the city water without much harm. The city's water mains and water towers served as the expansion tank. The bad part is potentially contaminated water from your house could be pushed back into the water main contaminating it.

For sanitation reasons many water meters now have built in check valves. Water can flow into your house but nothing can go out. So, when you bring cold water into your water heater it expands. With a check valve at the meter there is nowhere for that extra water volume to go and the water pressure in your house rises. This is why an expansion tank near the water heater is now required in many areas.

If your water pressure started out at 40 or 60 psi your house's plumbing could safely handle an extra 10 or 20 psi. When you are starting out at 90 or 95 you don't have much safety margin left. The T&P valve on the water heater or a burst pipe are the usual first points of failure/leakage.

The solution is two pronged. A PRV on the water main leading into your house limits the water pressure to a safe level. Then a expansion tank at the water heater accommodates the expanding water without causing a significant pressure rise in your house's piping.
 
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Old 12-05-19, 09:59 AM
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Thanks for the thorough and very clear explanation. I replaced the expansion tank with a new one. The old one was definitely waterlogged. The T&P valve is no longer leaking.

I'm still wondering about the water pressure. Do you think it was always as high as 90+ or could something change it? If it was always that high, I'm just wondering why we never had the issue before.
 
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Old 12-05-19, 10:28 AM
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Water pressure can change. Municipal water pressure is most often controlled by water towers. When the water level in the tower is lower the water pressure in the city pipes is lower. During times of low use the water tower fills and the greater height of the water creates greater pressure in the system.

Your house's location also affects your water pressure. If your house is on the top of a hill you will have lower water pressure than someone down in a valley. It's all about your elevation in relation to the water tower's water level.

If your town builds a new water tower or uses booster pumps. Your water pressure could also change.
 
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Last edited by Pilot Dane; 12-05-19 at 02:58 PM. Reason: changed top of hill
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Old 12-05-19, 02:03 PM
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If your house is on the top of a hill you will have higher water pressure than someone down in a valley.
I think you got that backwards
I live on top of a hill and have lower water pressure than anyone I know.
 
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Old 12-05-19, 04:08 PM
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Thank you for catching that. I've edited my post to correct my mistake.
 
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Old 12-05-19, 05:38 PM
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Interesting... I live at a lower point than most people in my neighborhood so that may explain it somewhat.
 
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Old Today, 11:05 AM
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Also, prior to the installation of a pressure regulator near where the main cold water pipe enters the house, the expansion may have pushed back into the water main so the pressure inside the house did not get so high.
Not all pressure reducing valves prevent the water from flowing back into the city system during a water heating cycle, the Watts valves I have each have a bypass in them just for this reason. However, since I installed my PRV here at home over 25 years ago and had no problem till the water meters were later changed and the new meters have a check valve. I finally just a year ago got around to installing my expansion tank. At the other house I installed a PRV 10 years ago as I replaced the 85 year old galvanized steel pipes with copper and everything has been fine till the past couple of months when they changed the water meter. Here we go again!
 
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