Hot water heater leaking at relief valve

[Larry Caldwell]

The check valve (backflow preventer) is the problem. It seals the system, so heat the water and the pressure spikes because the water expands. The expansion tank can be anywhere downstream from the check valve, but plumbing inspectors like it on top of the water heater. There is a 3/4" plug in the top of the heater to mount it, and all you have to do is buy one. Any place that sells water heaters can sell you one. They are cheap, about $30 plus fittings. Since your heater is tight against the ceiling, you can mount the expansion tank anywhere between the last valve and the heater.

 

[Frankenkubota]

Nobody wants to hear this so...i'm gonna say it.

my brother was a successful builder for 40 years and i was a grunt for many of those years.

when ever i said....."hot water heater" he would say

if the waters hot, why do you have to heat it?

right after that i heard....move that gravel!

 

[RBLapham]

you definitely need an expansion tank. With a backflow preventer the hot water needs someplace to "Expand", the pressure relief valve would be the only place and start dripping. When it is dripping turn on a hop water faucet and see if the dripping stops.

 

[drssg]

The check valve (backflow preventer) is the problem. It seals the system, so heat the water and the pressure spikes because the water expands. The expansion tank can be anywhere downstream from the check valve, but plumbing inspectors like it on top of the water heater. There is a 3/4" plug in the top of the heater to mount it, and all you have to do is buy one. Any place that sells water heaters can sell you one. They are cheap, about $30 plus fittings. Since your heater is tight against the ceiling, you can mount the expansion tank anywhere between the last valve and the heater.

This is where my lack of experience starts to bring out the devil in the details. Do you have thoughts on how specifically to connect an expansion tank on this installation?

I'm thinking that the most reasonable location is up by the tank. All other connection points are near ground level, and I would be afraid that it would get banged around with junk piled next to it.

The plumber that did the work used flexible screw on connectors, and that's about my speed, if that's an option.

I have successfully done some copper soldering in the past, but I don't consider myself good at it, and I understand that people use crimped fittings now.

The original expansion tank on our house water heater started to deform and hang down from its own weight. Another plumber installed a smaller expansion tank and added a support.

The smallest tanks I'm seeing are 2 gallons, and I'm guessing that's the appropriate size.

 

[Larry Caldwell]

The simplest thing would be to go to a store like Lowes or Home Depot and buy a book on home plumbing. An expansion tank should be full of air. I can see why the one in the picture got heavy, because laying it on its side let half of it fill up with water. Maybe there's a diaphragm inside that prevents that? I don't know.

Location is not critical as long as there's no valve between the expansion tank and the water heater. If you close the valve and isolate the heater from the expansion tank, the water expands and pop goes the PRV.

 

[GSVette]

Here’s a very simple, per code, expansion tank install in my shop.

 

[lman]

I don't believe code requires an expansion tank on a well system here as the bladder tank in the basement acts as the expansion tank. Is code different there?

 

[ponytug]

I don't believe code requires an expansion tank on a well system here as the bladder tank in the basement acts as the expansion tank. Is code different there?

The issue comes up when a hot water tank is downstream of a back flow preventer. That creates a sealed system and no place for the expanding (heated) water to go. So, you need an expansion tank to absorb the change in volume to limit the pressure rise.

All the best, Peter

 

[GSVette]

The issue comes up when a hot water tank is downstream of a back flow preventer. That creates a sealed system and no place for the expanding (heated) water to go. So, you need an expansion tank to absorb the change in volume to limit the pressure rise.

All the best, Peter

My inspector required it-so it may be another county based difference to the National code-like Studor valves (not allowed in my county) or one way floor drain valves in lieu of trap chargers on a floor drain as-also not allowed.

 

[drssg]

OK, this has officially turned bizarre. I decided to try a simple approach and just replace the pressure relief valve. Everything somehow worked fine for fifteen years, so maybe the new valve will last longer than the water heater?

I install the new valve, and even after the heater is on for several hours, I'm still getting cold water at the sink and the wash stall. I use my new PRV to remove a couple of glasses of water directly from the hot water heater, and sure enough, it's warm. I decide to give up for the night, and I shut off the power and water, and I open the hot water at the sink to relieve the pressure. It runs for a while - I guess due to gravity, since the heater is higher than the sink.

Low and behold, the water turned warm. So if the water is turned on, I get nothing but cold water. If the water is off, I get some hot water flowing down from the heater.

Here is a picture of the pipes, with arrows showing the normal flow of hot and cold water to and from the water heater.

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.

Unless somebody sees something I'm missing, I'm thinking it's time to bring in a plumber.