Hot water heater leaking at relief valve

[ponytug]

It never rains, but it pours.

At a guess, you have the inlet and outlet pipes switched on the hot water tank. If you didn't touch them replacing the pressure/temp relief valve, you have a bad mixing valve or it isn't plumbed right. The cold water inlet on your tank should be on the bottom. The mixer valve will divert 100% of the water that it thinks is hot to the outlet (stalls), so if you are getting cold at the stalls it either means hot and cold are swapped, or the mixer valve died. Since you were just working on the water heater, I would go with the pipes getting swapped. If you didn't monkey with the inlet/outlet pipes, I would double check that hot water is going into the correct port on the mixing valve. I have seen mixing valves incorrectly plumbed more than a few times.

All the best,

Peter

 

[BeezFun]

How did you turn off the water to the tank when you changed the PRV? Is it possible you didn't return one of those valves to the correct position and you have a pipe that is "backfeeding" either cold or hot water to the system rather than the heater being directly supplied. It would help to have a picture of where the hot water tank is in the piping- is it on the other side of that wall? And where are the shutoffs that you used to change the PRV?

There is an option to an expansion tank if you lack room. You can use a thermal expansion relief valve, but it will intermittently dribble water so you need to be able to plumb it to a drain. Here's one that sharkbite makes, so you wouldn't need to solder anything.

 

[drssg]

Thanks, ponytug. The only update I did was to unscrew the bad PRV and screw in a new one. Other than that, all the plumbing and equipment has been in place and working for the last 15 years.

I have a plumber coming out tomorrow.

 

[drssg]

How did you turn off the water to the tank when you changed the PRV? Is it possible you didn't return one of those valves to the correct position and you have a pipe that is "backfeeding" either cold or hot water to the system rather than the heater being directly supplied. It would help to have a picture of where the hot water tank is in the piping- is it on the other side of that wall? And where are the shutoffs that you used to change the PRV?

There is an option to an expansion tank if you lack room. You can use a thermal expansion relief valve, but it will intermittently dribble water so you need to be able to plumb it to a drain. Here's one that sharkbite makes, so you wouldn't need to solder anything.

There is a single shutoff valve for the tack room plumbing, which consists of a sink, a wash stall, and a hot water heater. There is no separate shutoff valve just for the water heater. The hot water heater pictured in the OP is immediately above the pipes in the last picture, and the same two vertical pipes are visible in both pictures.

To replace the PRV, I turned off the water to the tack room and the electric to the heater, then I opened the sink faucet to allow enough water to drain from the hot water heater, so it wouldn't leak water as I unscrewed the PRV.

Thanks for the link on the expansion tank alternative. I have a number of things to run by the plumber, based on all the feedback on this thread: the expansion tank, the PRV drain line, and a tray beneath the water heater for the day it begins to rust out.

I think I'll go ahead and have him replace the water heater. It has lasted quite a while. Once this is all fixed, I would like to not think about it again for a number of years.

At the same time, I don't want to come off as if I'm telling him how to do his job. I always found it annoying when someone who can't do my job tries to tell me how to do it.

 

[grsthegreat]

honestly, there are millions of homes without an expansion tank on them, and they seam to work well. i never had an expansion tank on my current home until i replaced water heaters about 8 years ago. then i added the expansion tank inorder to get rid of a very minor water hammer sound. it solved the sound issue.

my tack room WH does not have an expansion tank, and has not had one for 25 years. still works great

 

[BeezFun]

There is a valve near the top of this picture that blends hot and cold water to send warm water out to the wash stall. I'm thinking this valve is somehow allowing the cold water to go out the left side, so it is sending cold water into the hot water pipe. I don't know if that's feasible, but it's the only physical explanation I can find for what's happening.

I would agree, what you're seeing points to that valve failing, although in theory it shouldn't be able to fail that way. I assume that's a thermostatic valve, they are intended to prevent someone from being scalded by hot water. They have a spring inside that pushes a piston that blocks the hot water inlet until enough cold water flows to cause that piston to start moving and let some hot water flow. They're not supposed to fail in a way that would allow cold water to flow into the hot water side, but I guess anything is possible.

 

[drssg]

So the plumber came out today. I told him the whole story about the mysterious hot water that will only come out when the water is turned off. While I did that, he turned on the hot water in the tack room sink and let it run for a bit. When I got to the part about my suspicion that the temperature valve was somehow allowing cold water to flow into the hot water input, he reached over and adjusted the temperature setting on that valve. Two seconds later, hot water flowed into the sink and he said, "There you go." ..... I mumbled a mild profanity.

He didn't say that this is how it's supposed to work, but he didn't seem surprised by it. I was too gobsmacked to ask follow-up questions. I would have sworn that the valve would only affect the water temperature in the wash stall, but I confirmed that setting the valve to the cold setting also causes the hot water at the sink to turn cold.

He felt that someone must have turned the dial to initially cause the problem, but it's just me and my wife here, and neither one of us touched it. He seemed to be a minimalist, and his recommendation was to just leave everything as is until the water heater eventually starts leaking. Even though it's fifteen years old, we don't use that much hot water in the barn, and it could potentially last a long time.

Part of my concern is that I still don't know what initially caused the PRV to leak, and I don't know whether it will repeat in another week. We have had a low-priority desire to replace the sink and faucet anyway, so I think we'll go shopping for that. We'll also pick up a new water heater, an expansion tank, and a tray for the water heater to sit in. Then we'll call him back to install all of it, and I'm hoping I won't have to deal with this again until I'm an old man.

FWIW, the following link describes the valve in question. I don't see anything in the specs that would suggest to me that cold water would or should flow out the hot water input line. Go figure.

https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/20250-source/es-70a-pdf

 

[Wakey]

Well, it’s sorted!

I replaced a water heater a few years back. Glued the pipes and had a quick lunch. After I sent my girl up to the street to turn the water back on. POP! splash! “Turn it off!”

So I cleaned the mess with every towel I own and reglued the parts. This time I was going to wait more than 45 minutes because I won’t be stupid twice.

Repeated soaking..

Tried again.. New pieces and parts...

Pop.

It is now Saturday evening and I kind of had my heart set on a shower so I called a plumber.

He came out and did exactly what I did and we waited about 15 minutes.

Turned on the water and.... All is well.

He said that sometimes you get a bunk can of glue. (I bought it when I picked up the water heater)

That knowledge cost me $185.00

 

[grsthegreat]

Glued pipe on hot water system... now that’s something I have never seen before

 

[ponytug]

If you use CPVC pipe, you can use that on hot water lines. However, it does take a different glue. (Might explain @Wakey's issue.)

I think that PEX is better, but it hasn't been around as long in the US.

All the best, Peter