Water pressure too high after using hot water

My house is about 8 years old. All original plumbing and 50gal natural gas hot water heater.
About 3 months ago, one morning after taking a shower, the whole house filter I have near the meter in my basement burst.
I had a plumber come out to replace the broken filter system with a new one. He said while he was there, he noticed the pressure was a bit on the high side (70ish) and backed it down to 50 using the PRV.

Since that day we experience very high pressure after running the hot water (shower, dishwasher, clothes washer, etc). The way we noticed is that now after using the hot water, our kitchen sink and our shower head would drip until we opened a faucet somewhere to relieve the pressure for about 10 seconds. In the 7 years of being in the house prior to this day, we never had a problem with the pressure.

Last night I bought a pressure gauge and ran a few tests:
I ran only cold water for about 5 minutes. Shut everything off and checked the pressure. It held steady at about 45psi.
I ran only HOT water for about 5 minutes. Shut everything off and checked the pressure. It started out at 45psi and about 10 minutes later was over 160psi!

I do NOT have an expansion tank near my water heater (or anywhere, for that matter).

It seems that adding an expansion tank would solve the problem. Does that seem right?

And if so, can anyone explain why all of a sudden we have this problem? Why did we not have this problem for the prior 7 years?

Any help would be greatly appreciated.

Thanks!

Your symptoms could indicate need for an expanson tank for the WH, but also, and more likely based on the circumstances, your PRV is bad. A slow leak past the diaphragm allows house pressure to slowly build up to equal street pressure. Each time a tap is opened, it will return to "set" pressure.

With a PRV, you need an expansion tank on the water heater.

Ditto the Expansion tank. A tank is always required when a PRV and or check valve is installed anywhere after the meter.

You have correctly diagnosed your own problem - congratulations!

I had the same exact problem until putting in an expansion tank - now the pressure stays at 60 psi regardless of hot water use.

Interestingly, where I live (Omaha, NE) the need for expansion tanks is still not common knowledge. I had one owner of a private plumbing supply house recommend I get a higher pressure temperature/pressure relief valve for my water heater since the old one would trigger when the house pressure got too high!

Talk about treating the symptom but missing the actual problem.


When you do put in your expansion tank, I recommend also putting in a hose bib (so you can monitor the pressure) and also a 1/4 turn ball valve to isolate the tank. Eventually the rubber diaphragm will fail and the tank will fill with water. When that happens, if you have that ball valve in place, it becomes a really simple matter to replace the tank without shutting off the whole house water.

Also, make sure the tank is adequately supported, since it will eventually fill with water (and get to be pretty heavy).

The thing that is bothering me the most is why is this just all of a sudden, after 7 years, becoming an issue?
Why have we never noticed high water pressure before now?

Thanks for all your comments so far!

You probably never noticed it before as the excess pressure was venting itself elsewhere. When the filter was replaced it may have tightened up the system. I went twenty years under the exact same circumstances and had never heard of thermal expansion. One day the whole house filter started to seep and replacement parts were no longer available. I had the filter taken out, and since they were in the same area, had the PRV valve replaced as well....just because it was old. Thought also, since I was doing all this stuff, that it'd be a good time to replace a 12 year old water heater. With everything new, and the system tight, I learned all about thermal expansion within 24 hours.......valve on the WH started seeping.

Mort

Mort said:

You probably never noticed it before as the excess pressure was venting itself elsewhere. When the filter was replaced it may have tightened up the system. I went twenty years under the exact same circumstances and had never heard of thermal expansion. One day the whole house filter started to seep and replacement parts were no longer available. I had the filter taken out, and since they were in the same area, had the PRV valve replaced as well....just because it was old. Thought also, since I was doing all this stuff, that it'd be a good time to replace a 12 year old water heater. With everything new, and the system tight, I learned all about thermal expansion within 24 hours.......valve on the WH started seeping.

Mort

Click to expand...

But if the PRV was the source of the problem, wouldn't it occur ALL the time? Not just after HOT water was used?
As mentioned in my original post, the pressure only builds up after running hot water for a few minutes. If I only run cold water for a few minutes (after the hot water heater was no longer heating new water), the pressure stays consistent at 45psi.

Thanks.

When you run hot water, then the burner comes on to reheat the incoming water.
As it heats, pressure can build.

So another question may be, is the thermostat on the water heater set right? Or could it even be faulty?
What is the temperature of the hot water?

It's not uncommon for Pressure reducing valves to wear out after a while though.

Another question....
For a tank water heater... lets say for argument sake the actual internal tank is 5 feet high. When the tank is filled with water, is it filled all the way to the top at 5 feet? Or is it filled only to say 4 feet, leaving a bit of space open that is meant to allow for expansion of the water from heating it?

When the water is heating, should the cold inlet line get warm? If yes, how far up should it be warm? 6 inches, 12 inches, etc?

Thanks!

The water comes out of the top of the tank.
If there was air there, the water would have to leap up into the pipe.
But water doesn't leap like that.

The entire tank is full of water.

For expansion, you add an expansion tank, those have rubber bladder in them, and a schrader valve that allows you to pump air into the back side of it.




The cold water inlet will get warm. Heat tends to rise.

SteveW said:

I had one owner of a private plumbing supply house recommend I get a higher pressure temperature/pressure relief valve for my water heater since the old one would trigger when the house pressure got too high!

Talk about treating the symptom but missing the actual problem.

Click to expand...

Sure this guy was a plumber??

He claimed to be - said he'd been in the business for 30 years - and then proceeded to berate me when I tried to politely question the use of a higher-pressure TPR valve instead of an expansion tank --

"You don't need that thing!"

I left as quickly as I could...

I measured the hot water temp out of the tap. It is at 120F which is what I set it to about 5 years ago.

The thing I keep coming back to is, why did this just start happening a few months ago? I can't seem to find or find anyone who can explain it.

Oh, if it helps any... I checked the pressure at my neighbors house. His pressure is at 60. We ran the hot water for 5 minutes and checked again, The highest it got was 78. Now, he does have a water heater that is only about 1 year old and a Pressure Regulator that is only about 2 years old.

So, could a water heater that is "going bad" cause this sudden increase in pressure?

Get a pressure gauge and attach it to a hot water faucet. Measure the pressure. Now, open another hot water faucet and drain enough hot water to trigger the heater to kick on and watch the pressure gauge. Usually this will trip the TP valve. It's just basic physics. Water expands when heated. If it can not expand into the water supply system, then it builds up in the tank. The PRV is also a check valve that prevents the expansion from being absorbed by the city main. That's why you need an expansion tank.

If you changed anything - added a shutoff to your clothes washer, changed the fill valve on your toilet, anthing that might have been leaking slightly when the pressure rose, you may never have noticed. It is also possible the city added a new pump and your static pressure is higher, or added a check valve on the supply or changed the meter which now has one built in.

Regardless, if you are getting a pressure buildup when the WH turns on, the prescribed fix is an expansion tank. You should have had one when the PRV was installed. If the T&P valve on the WH got stuck, you could blow up the WH, create all sorts of problems.

No, It sounds like a classic closed system in need of an expansion tank. It also sounds like the T&P doesn't work!

Same answer pasted from the other forum you posted in... Yawn

The PRV's I use claim they have a built-in internal bypass to bleed back excess pressure, but I don't think you're supposed to rely on that.

I suspect you are the same person who posted this on another board...
After 30+ responses the answers there are still the same....
Replace the T&P valve and put an expansion tank in....

You may find the T&P tripping at less that the 150# rating on it.

If so replace the T&P and install an expansion tank.