Hot water seems to be putting pressure back into my house plumbing system.I have heard that a exspansion tank would help.What are my options,where should I buy this tank and how should it be installed.
Thanks
Mike

Your first order of business should be to measure your water pressure with something like this: Water Pressure Gauge w/ Garden Hose Adapter - FreshWaterSystems.com

It should be about 55 PSI.

Next, you should know if a PRV (pressure reducing valve) or backflow preventer is installed. These would probably be installed at the meter. They could have failed.

Some PRV's may not require an expansion tank, but a backflow preventer does.

First, determine if you need the PRV. Measure cold pressure after running some hot water.

Next, you can start with a cold hot water tank, run a small amount of hot water, turn on water heater, don't use any water, and remeasure the pressure.

The expansion tank needs to be on the cold water side after the main shut-off valve. Near the water heater is common, but it can be anywhere.

The expansion tank goes between the water heater and the shut off valve for the water heater on the cold side. The air bladder inside should be set at the water pressure of the house or just slightly over. Maybe a couple of pounds. Most come precharged at about 40 psi which is rarely high enough. I believe they sell them at the box stores, and most good hardware stores.

Thanks for the response.I have contacted the water company to see if I have back flow prevent-er at the water meter.Still haven't heard back from them.
I have measured my pressure at a outside faucet and it goes from about 50 psi up to 140 psi.It seems to build up to 140 psi slowly after a period of non use.My incoming pressure from the water meter to the house is 140 psi. I have a regulator at the house which is set for about 50 psi. If I turn on a faucet,either hot or cold the pressure immediately goes down.It gradually creeps back up to 140 psi.It sounds like thermal expansion and that I need the aforementioned expansion tank.Thanks for the feedback.Do you think the expansion tank will fix my problem.

Thank You
Mike

Yes

If it's getting to 140, then at least you know that whoever did your plumbing must have done a good job! Not sure my amateur soldering would handle that.

Turn your water heater to pilot and run water to bring your water pressure down to 50 psi. Does your water pressure still rise with the water heater set to pilot? If yes, you need a new pressure reducing valve. If no, then you should turn your water heater back to on and see if the pressure increases to 140 psi. If so, you need an expansion tank. That much increase in pressure sounds like a LOT of thermal expansion if that is the case. Sounds like too much to be thermal expansion and it is coincidental that it goes to 140 just like your incoming pressure before your meter.

Sounds like your pressure regulator is not working, if your pressure drops when you turn on a faucet then creeps back up to 140 psi then its not regulating the pressure correctly. How old is it? May be time for a new one.

You say you measured pressure at an outside faucet. Is that faucet before the pressure regulator, or after?

Hard to imagine a municipal water system at 140 psi. Is that normal?

Thanks for the replies all.The county checked my water meter and told me that it doesn't have a back-flow prev-enter.Our house is close to 30 years old and the water meter is an older one.I believe the codes changed over the years and perhaps newer homes are required to have newer technology.They did tell me that some of the older meters might not read the correct water consumption.They have had people replace there meters with newer ones and saw there water bill spike up when the new meter started reading correctly.
Back to the current problem,our water pressure from the county is 140 psi.It used to be around 120 psi but for whatever reason they boosted the pressure.I'm measuring at an outside faucet which is on my regulator and its set at about 50 psi.When water is being used in the house that pressure is shown as approx 50 psi at that faucet.When there is a period of non use in the house like overnight the pressure creeps up to 140 psi.From what I'm understanding this could be a result of thermal expansion from the hot water heater and I'm think at this point that's probably what it is.At least it's a good place to start.I have a 50 gallon water heater.Is there a specific size expansion tank that I would need.what other considerations do I need to think of.Thanks for the input, thanks for taking the time to respond.Sorry for the long post.Old guy that's almost retired.

Thanks
Mike

Tanks are sized by design pressure (what your regulator is set at) and water heater size. Manufacturer dependent sizing tables.

See: PlumbingSupply.com - Water heater thermal expansion tanks

There are two types: diaphram and bladder

Expansion tanks never hurt to have. You do not need a large tank. I think the one I normally install is 2 or 21/2 gallon. Make sure to install it on the cold side of the heater between the heater and the shut off valve for the heater. Also be sure to set the air pressure inside the tank to slightly over 50 psi, since 50 is your normal pressure.
I do not think this will solve your problem though. I think you will find the pressure reducing valve needs to be replaced as well.
Good Luck!

Seems strange to me that your pressure seems to creep up to exactly what the pressure is for the water system. I think I would have to try turning off the water heater one night and seeing if the pressure rises or not. If it does, then the pressure regulator would seem to be the problem.

That is pretty much what I said in post #7. Try what jlisenbe is saying.

Had the same problem - ugh.

I have an older home, '20's. The city switched us onto the "newer mains". AND - reran my main; killed two of my trees and cut my sewer main... that's another story.

Had to install a PRV to regulate the incoming pressure, and install an expansion tank for the hot water expansion, since I put in a backflow prevention valve. All is well now. All that wasn't necessary before they "fixed" my incoming pressure. (it was 120psi).

If your pressure was 120 psi you would have been wise to install a PRV long ago!

The very first thing you should do is get your house pressure down to the normal house pressure of40 to 60 PSI. This means installing a PRV, (pressure reducing valve) (see image) ar the point where the service enters your house. You may also have to add a expansion tank on the cold side of your water heater. A PSI of over 80 PSI will put a strain on the joints in the water pipe and damage your faucet cartridges. Install a PRV ASAP. Good luck, To,m