High water pressure despite new PRV and new expansion tank

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Hungry4Pizza

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Hello, I am in need of some additional guidance. Let me preface by saying that I am not a plumber, but I do enjoy expanding my skillset. I’ll start by walking through the problems, some solutions I’ve implemented thus far, and where I’m at now. I’ll also give as much detail as I can.
My water pressure seemed very high. My house is 30+ years old. We’ve seen some side effect of the high pressure like the safety relief valve dripping, some minor leaks at the water heater connections, and a dripping sink faucet. I bought a Watts pressure gauge and measured at my laundry sink. The pressure reads above 110psi. My initial thought was to replace the PRV, so I did. I bought a 1-to-1 replacement. I checked with the city to make sure that the incoming water pressure didn’t exceed the max pressure of the PRV. The city provides 124-128psi. My PRV is well suited with a max pressure of 300 psi. I made sure to install the PRV with the marked flow arrow in the direction of flow. After installation, the pressure did not subside. The PRV was supposed to be preset to maintain 50 psi at the outlet. We’re still in the 110’s of pressure, which was no change from the initial readings.
My next step was considering other factors, which was thermal expansion from the water heater. There was no expansion tank installed. To test my theory, I turned off the water heater and shut off the cold water supply to segregate the water heater from the cold lines. Bingo! My pressure was now measured at 75 psi at the laundry sink. I was finally getting some improvement. The PRV setting was supposed to be 50 psi, but I was getting 75 psi. Next, I bought an expansion tank. Based on the manufacturer, my 50 gallon water heater and an inlet pressure of 75 psi required a 2-gallon tank. I pre-charged the tank to 78 psi before installation. (just a little above the inlet pressure). I installed the tank per the manufacturer. Upright position on the cold water side of the water heater. I used 3/4” brass pipes and fittings. After installation, and before turning on the water heater, I checked the pressure which was good at 75ish psi. After turning the water heater on, the pressure creeped up to 110 psi again. I thought that may be normal while the water is heating up and the tank acclimates to the new pressure. We have used hot and cold water throughout the house to allow the PRV and the tank to both do some work. It’s now been a couple hours. The water heater is not heating and there are no faucets open. The pressure at my laundry sink is 110 psi again. I’m at a loss for what could be the next logical step. Any advice would be greatly appreciated. I’ve attached pictures of the expansion tank installation and manufacturer data sheet as well as the current reading of 110+psi.
 

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We always install only double union PRVs because even new, there are some that are defective.
And in the future always install a tee and hose bibb before the expansion tank to make changing out less of a mess when the invariably fail.
BTW, teflon tape is not used or needed on WH flex connections, it is only a rubber washer seal. The threads just hold the joint together.
 
We always install only double union PRVs because even new, there are some that are defective.
And in the future always install a tee and hose bibb before the expansion tank to make changing out less of a mess when the invariably fail.
BTW, teflon tape is not used or needed on WH flex connections, it is only a rubber washer seal. The threads just hold the joint together.
I did neglect to attach a picture of the PRV. It has a union on the inlet and FPT outlet.
Good advice on the tank. If I need to make any more corrections, I’ll incorporate another tee before the tank.
Now that you mention the flex connectors, I do recall seeing the rubber washer in there. I guess I wasn’t thinking in the moment. Thanks for your reply!
 

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Be VERY careful if you are fiddling with that PRV because I see what looks like could be PVC Sch. 40. PVC is not allowed inside a dwelling because it becomes brittle and cracks easily and the male threads can shear off as you blink wrong.
You definitely may be able to spin the PRV off, or you could also try a rebuild kit, but, I never rebuild after having no success on multiple rebuild attempts over the years.
 

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