Water heater pressure

Folks,

Hope you can help alleviate some concerns I have about my hot water heater.

Quick background--

Recently replaced dip tube, anode, drain valve...had lost dip tube and this work gave us full hot water again. One week later, yesterday, found water...TP valve had opened. Replaced it this a.m., but used a 125 psi one instead of the 150 psi since the hardware store only had 125 and 175.

Anyway, all back and running.

But, I added a pressure gauge to the drain and have been wondering if I have an issue.

First, the nominal pressure reading when using hot water is 50 lbs. Just after calling for hot water and turning off the faucet, it rose to 111 lbs.

I don't know if I have an open system or not, but there is an 'upside down cone' shaped brass fitting between the main valve and the water meter, I don't know if that's a pressure reducing valve or not, and I don't know if they and/or water meters all have check valves in them or not.

Also, I have an expansion tank that 'appears' to be tied into the system, but I'm not sure. It's approximately 1' diameter flextrol, that says WP 100 psi.

This tank is connected to a 'T' that also receives a 1/2" line from cold supply, and the 1 1/4" supply side line from our hot water radiator heating system.

So, would that tank actually be involved in controlling pressure from the hot water heater as well as radiator heat, and if it's only rated for 100 psi, and I know my water heater gets to 112, does it need to be replaced, or do I need a second expansion tank?

Also, if right now I've been living with 112 lb hot water pressure for 15 years, do I need to change my T/P valve to 150 lbs as was originally on tank, or is 125 lbs. likely to be fine. A spill wouldn't be catastrophic, just a nuisance!

Thanks again guys...can't tell you how great it is to have a forum like this...you've helped me build a bathroom and save thousands!

Okay, gotta check tank pressure!

Thanks again!

Doug in NJ

You want to get the right T&P.

Below is a picture of a pressure reducing valve.




You should maintain less than 80PSI on the system. You need to figure out where the pressure increase is coming from. Whether it is a need for or, failed PRV or, a thermal expansion problem.

Thanks Redwood!

Okay, I'll get a 150 lb one as soon as I can. So that picture is of what I have, so presume I do have closed system.

Is it okay that my gas water heater gets up to 112 lbs of pressure? I know it's rated for 150, but I'm also a little concerned because I'd used a magnesium anode to replace my old one, which was largely gone, and heard that it could create hydrogen if the inside of my tank is rusted (it didn't appear to be when I'd inspected with TP valve replacement).

Anyway, thanks again...will get valve...maybe expansion tank depending on what you all think!


Doug

If you have the valve you have a closed system and need an expansion tank.
You may have a closed system even without the valve.

The key is knowing when the pressure increase ocurrs. Does it happen only when the water heater is heating?

Quick clarification if needed. The 112 lbs. I'm getting is from the hot water heater itself...on the drain valve of the gas hot water heater itself...with all faucets off of course.

Should I also measure faucet pressure; I'd expect it to be a bit lower, but don't know?

When faucets are open, the gauge reads 52 psi, so that's my supply pressure, I assume, so think the PRV is probably okay. Is that right?

Doug

Crossed, posts, Redwood...sorry and thanks!

Yes, it only goes up to 112 when it's heating. I just turned the faucet on for a second...cold water faucet for 2 secs. and pressure dropped to 80. Hot water turned on for a second, pressure dropped to 60. Since it's not heating right now, it's stable at 60.

Hope that tells you something that's useful!

You need a properly working thermal expansion tank on the system.

I do have an expansion tank...filtrol model 110...WP 100 psi, charge pressure 12 psi (and I checked the pressure, it is 12 lbs....and there's no water coming out).

So I guess the real question is that if this system has been working fine for the 15 years I've been in the home, and the expansion tank otherwise appears to be working, is an increase in the water heater tank pressure an issue, as long as it doesn't go beyond it's limit and/or the TP valve limit?

Sorry, I'm obsessive and want to do the right thing!

Doug

It sounds like that expansion tank is connected to the heating system (you said it was connected to the line the radiators are connected to), so yes you also need an expansion tank for the potable water system.

An expansion tank for the heating system would normally have somewhere around 12-14 pounds of pressure and aren't designed for potable water or the pressure of it.

What doesn't make sense is your statement that the cold potable water also connects to that tank. You sure? Maybe a picture would help.

Hmmm, so this house survived for 50 years without expansion tank where one was supposed to be...been living on borrowed time I guess! LOL

No, drinking water doesn't come through the same line directly...sorry.

What I meant was that the supply into the T for the radiator boiler came from a split that feeds the hot water heater. I was thinking, I guess, that the pressure from the water heater would just spread out wherever it could and eventually hit the expansion tank.

So, if the water heater periodically hits 112 lbs., that's what the hot water faucets are, periodically, holding against, is that correct...or has the pressure diminished from the hot water heater by the time it gets to a faucet by expanding all the copper piping in between?

Doug...sorry if I'm too curious and too ignorant!

Water doesn't compress, so it only takes a little expansion to raise the pressure. The pipes, hoses, etc. actually expand a little to compensate until something lets go, if it gets high enough. Often, the first thing is the T&P valve. If you have a closed system, that increase is going to happen UNLESS there's someplace for it to go, thus the expansion tank. In an open system, it actually goes back out to the supply. That tank needs to be big enough for your system and be charged up to the normal, static pressure.

You seem like such a trustworthy guy, I guess I'll believe you!

I'm still curious, just for curiosities' sake, whether my situation is so uncommon...also, come to think of it, why didn't the inspector notice that when he inspected the heater installation five years ago? So, next question: is it possible I can have a pressure relief valve before my water meter that doesn't have a backflow valve and that's why I don't have an expansion tank?

D

The whole idea of needing thermal expansion tanks is new to some parts of the US (like my state, Nebraska) - when I went to a professional plumbing supply house to buy fittings to hook up my expansion tank, the counter guy thought I was on Mars to even worry about thermal expansion. So - not surprised that this may not have been picked up on an inspection of your house.

The symptoms you are describing (rapid increase in water PSI during a period when water heater is heating up a slug of cold water) is classic for thermal expansion. If you open any faucet, hot or cold, anywhere in the house, for even a second, the pressure will come down to normal.

Since I put in an expansion tank, I've noticed that faucet washers last a lot longer than before, and my old Sears water softener has worked for several years without replacing internal parts (in the past I had to overhaul it every year).

High water pressure really takes its toll on all your fixtures.

Well, this seems like a good time to do it all...I'll be replacing the TP valve with one at 150 psi...not a lot more to cut in an expansion tank.

Anyone happen to know if it's floating in a 3/4" copper pipe that spans about 5' total, whether there'd be any issue with its weight--I think I'll need about a 3-4 gallon tank...

I found one with pre-charge of 40 psig. Sorry to ask, but is that 40 psi for each gallon? Also, should I pump it up to higher pressure or how would I find its proper pressure--anyone with URL or thread to save me some time?

thanks to all!

Doug

All you need is a 2 gallon tank unless you have 80 gal or bigger water heater.

The precharge should equal the working pressure of the water system.

The tie in for the Expansion tank should be between the valve on the cold supply to the water heater and the water heater inlet. The tank may be remotely mounted. It must be rated for potable water.

Watts Termal Expansion Tank Installation Instructions

When it fails, and they all do eventually, it will fill with water so you want to support the thing for that eventuality. Check the air pressure with a tire pressure gauge BEFORE you hook it up and adjust with a bicycle pump. Since it doesn't hold much air, it's too easy to overinflate it with bigger things unless you have the touch from experience.

Thanks again guys. Guess I have some work to do!

One thing I have to check, though, is whether I actually do have a backflow check valve...so if anyone is still reading this...

I do have the PRV, but don't see another fitting inline between shutoff and meter. Is a check valve integral to the PRV...mine looks just like the picture Redwood posted above. Our home was built in 1957, and although I know the water meter was replaced at some point, the PRV doesn't appear to ever have been.

Also, any issues using compression fittings over sweating? I'm sure there are some strong opinions here...and I'm willing to listen to them! Since it'll eventually fail, I'd like to make replacement easier.

Cordially,

Doug

A PRV, by design, has a check valve in it. Now, some do have a high pressure bypass, but depending on what your incoming pressure is, may still be too high for your system and give you grief. IF yours has this, water can flow backwards IF the house pressure exceeds the incoming water pressure. Safest thing is just install an expansion tank. Won't hurt, and is required in some code enforcement areas, and will solve the problem if the utility ever installs a check valve either in the line or as part of a meter upgrade.

I think you need to update the things you are using. just like what jadnashua say

A PRV, by design, has a check valve in it. Now, some do have a high pressure bypass, but depending on what your incoming pressure is, may still be too high for your system and give you grief.

Click to expand...

All done, guys!

Added 2 gal. expansion tank, pumped it up to supply pressure of 52 lbs, and now, I'm sure you know, my pressure in the hot water heater is only 60 lbs, not the 112 it was before.

So I thank you and my pipes/fittings/etc. all thank you!

Doug