Water Heater Pressure Relief Valve

[MistWolf]

Recently got a new water heater and the pressure relief valve keeps dripping. Although the valve is new, I replaced it thinking maybe something got caught in the valve seat. The new valve drips as well.

The valve is supposed to relieve pressure when it reaches 150 psi and when water temp reaches 210 degrees f. I drained water into a bowl and measured the temp at 128.5 degrees f with a digital cooking thermometer. Any idea what's going on? Do I need to regulate the pressure of the water going into the water heater?

Thanks

[willie]

Since both leaked, that indicates that they were performing the task for which they were designed. If the city put a pressure regulator at the street to prevent excessive pressure from damaging plumbing, then when pressure builds in your tank, it can't alleviate pressure by pushing tank water back into the cold water line. I suggest asking the city or a plumbing company if your line has a regulator. That's my guess.

[hufnagel]

Do you have an expansion tank? if not you should contact the contractor that installed your new water heater and ask why not. IIRC it became code that you need an expansion tank if you're structure has a pressure reducing valve from the main, on or around 2015. I just went through a similar problem where I was having excessive pressure build up (160+ psi at one point) due to a combination of failed pressure valve and lack of expansion tank.



post expansion tank install, and water heater servicing (replaced inlet, outlet, anode)

eta: and yes, I do my own work.

[dsa]

I recently had the same problem on a < 1 yr old water heater. I immediately thought I was experiencing excessive pressure. Turns out expansion tanks are cheap and fail often according to a fellow shooter who is a journeyman plumber. Replacing the expansion tank fixed the problem.

[SoCalDep]

I've gone through a couple water heaters due to failure of the pressure regulator from the main water source to my house. The water pressure going into my home is way to high, and the regulator puts it where it needs to be. When that fails, the water heater is sure to follow. I try to pay attention to water pressure in the home and a pressure gauge isn't very expensive. If it's the regulator, changing/repairing the water heater won't solve the problem and you're setting yourself up for the same issue.

Now... I have no knowledge in plumbing except for what I've managed to break, so grain of salt and all...

[MistWolf]

Thanks to all. I know very little about plumbing. There is no expansion tank. What does the expansion tank do?

I'll have to look to see if there is a pressure regulator.

[shootist26]

Thanks to all. I know very little about plumbing. There is no expansion tank. What does the expansion tank do?

I'll have to look to see if there is a pressure regulator.

What does water do when it gets heated? It expands. Now where does the extra volume of water go? there is nowhere for that water to go other than out the T&P valve.

An expansion tank has a rubber diaphragm in it that divides it in half. The half opposite the inlet is just pressurized air. Look up a cross section picture of it and it will be clear how it works. Very simple device. Basically it gives the water a place to go that isn't out your T&P valve.

[MistWolf]

I installed an expansion tank and pressure gauge. Pressure in the water line is 80 psi. So far, the drip has stopped. Thanks, everybody!

[Jack Ryan]

I installed an expansion tank and pressure gauge. Pressure in the water line is 80 psi. So far, the drip has stopped. Thanks, everybody!

You are on the high end pressure wise for domestic water systems.

The problem you are experiencing is common to our area as we have rural water utility and it must serve both the people at the top of the hills AND the people at the bottom of the hills.

In the old days the utility would have people on the high ground or the end of the line complaining of no pressure. After years of complaints they put in booster pumps. Since then people in the valley have had to all put in pressure reducing valves to prevent leaks and situations such as yours. Many waited until after "the flood" to take preventive measures. Even with PRVs it is still a common occurrence to hear of people getting over pressured their system causing leaks and ruptures.

PRVs go bad. They don't last for ever and they can be over come by short bursts of high pressure. When opening water lines such as putting long lines back in service after repairs, it is important to crack the valve and let it fill up before fully opening it. If you just spin a valve open on an empty line the water will rush in like a truck down a high way and when it hits the end, the same thing happens as when a truck hits a bridge abutment. Something is going to give. In the case of a 12 inch water line filling full open to the end it will sound like you hit it with a sledge hammer. That pressure goes straight in to your house system. Usually making something in the hot water system leak first. The same lines rated for 120psi cold water are NOT rated that high for HOT water and the pressure release SAFETY on you water heater is normally the lowest pressure point because it is intended to "leak" if it goes over pressure.

Water does NOT compress like air will, that is what the expansion tank is for. It allows for some cushion when you and your family are spinning valves open and closed turning water on and off. With out one, that is when you hear the pipes "clang" if you spin the bath tub valve closed fast. This may also make pipes move and vibrate creating weak and worn spots in plumbing lines.

Having lived the situation 20 year, you are facing now and having decades experience in industrial power houses and water utilities I do have some suggestions to deal with it and prevent facing a messy leak situation. Any of which may just be kept "in mind" for when you may have a plumber there any way of pretty easy DIY projects.

1st you need and inside shut off that is easily accessible. 2nd thing I'd put down stream of the shut off where it is easy to get to is a sediment filter. This will protect the rest of your plumbing from getting foreign particles from under the seat of any valve you shut and protect you from malfunction of a PRV which I suggest be next down stream of the sediment filter and reduce your house hold pressure to about 60 psi. With a gauge right after so you may confirm occasionally all is functioning properly. Pressure may drop a couple pounds if someone is using water in the house but anytime that gauge is going over your setting, I'd get that PRV checked or replaced. It is your back up protecting you from what ever the water company might do.

I have all this in the basement right next to the water softener where it is easy to keep track of and keep a running log book of softener use and all the rest. In an instant any one in the house can see if anything out of the ordinary is going on there.

[HC-7]

Hufnagel, I installed a Chinese Anode rod, it has a dome shaped top, denoting it is magnesium.....After a couple of months my washing machine mixing valve clogged....Replaced the valve, it happened again....My Anode rod was not dissolving, it broke down to coarse size particles....New Chinese anode rod was installed , I have the same problem...The fix was to install a whole house 5 micron water filter, after the water heater....As it is a clear bowl, I can observe how much magnesium I catch....filter is replaced every 4 months....regards....alex