Water Heaters - Installed Thermal Expansion Tank, PRV still leaks occasionally

Just installed a new Thermal Expansion tank this weekend and also replaced the PRV on my 40 Gallon water heater. After installation, it helped out a whole lot and the PRV only dribbles a little bit occasionally, after the pressure has built up for a couple hours.

My question is, what could be wrong? I thought a Thermal Expansion tank would resolve the issues of expansion and the leaking PRV? Could I have precharged the tank incorrectly? Maybe I just need a bigger tank? What else could need fixing?

you may want to take the water pressure at a hose bib

Did that, and looks like water pressure still builds up to 140 or so

Did that, and looks like water pressure still builds up to 140 or so

140 lbs is way too high, you need a pressure reducing valve, most codes require a max. of 80lbs. Most PRV valves are set for 150lbs, it takes very little thermal expansion to exceed that limit when you start with 140psi..

The tank should be charged to the incoming water pressure, but with your excessive pressure this does not apply.

Bottom line is you need a pressure reducing valve, make sure that you have a pressure gage on the supply side of the prv. Lots of luck.

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"If all else fails, read the directions"

Is your normal operating pressure 140#, or just when the system is bottled up and the water heater is operating? Also, are you served by a municipal water system or do you have your own well?

If you're on a municipal system, do you know if they have a pressure reducing valve or backflow preventer on your incoming water line that is not allowing the thermal expansion to backpressure into the municipal distribution system?

It builds up to 140 after not using it for a while and the water heater cycles. normal operating pressure is about 40. I thought installing a expansion tank would fix it but the problem continues. I am on municipal water and there is a pressure reducing valve, however, which is why I'm thinking it's a bad PRV?

How high do you have the water heater set at. 40 psi water to 140 psi after the water is on. Dont sound right. The tstat in the heater ok????

water heater temp is set to below the "normal" setting mark on the dial, and i measured it to be about 125 degrees.

Just installed a new Thermal Expansion tank this weekend and also replaced the PRV on my 40 Gallon water heater.

Ok Did you check the air side of the tank before you put it in??????? With no water pressure on it . The air side should have 38lb psi in it

Yup. Checked the air pressure in the tank before and made sure it was right at 40ish.