Water pressure too high after replacing water pressure regulating valve

[bbatl]

Several months ago we had faucets dripping, thumping noise in one faucet and a small dripping leak in a pipe in the basement. The plumber measured the water pressure outside at the tap we use for the garden hose. It was at around 85-90psi. He said we needed to replace the water pressure regulator valve. He performed that repair and adjusted the water pressure (I think he set it to 65). A few days ago we started experiencing the same symptoms: water bursts out when I open a faucet, thumping noise in one faucet etc. We left a water pressure measure gauge attached to that outside tap for 24 hours. It showed 100psi. We called the same plumber and he said that this is probably due to the expansion tank failing. Is that even possible? My understanding is that the expansion tank is for hot water only : "The expansion tank’s purpose is to protect your house’s hot water system from excessive pressure". The outside tap never gets any hot water. So my question is: is it possible that the high water pressure is due to the expansion tank failing or is this purely an issue with the water pressure regulating valve?

Thank you,

 

[Reach4]

My understanding is that the expansion tank is for hot water only : "The expansion tank’s purpose is to protect your house’s hot water system from excessive pressure".

While it is the water heater that causes the high pressure, the pressure affects all of your plumbing after the PRV. So I think that the part you put in quotes is inaccurate.

Note that when you are using a little water, the thermal expansion tank should be empty. When you are using a little water somewhere, the water heater expanding water is not a factor. Knock on the tank to learn what empty sounds/feels like. If the PRV regulates to 65 PSI, I would set the air precharge with zero psi water) to 67 PSI. There is not uniform agreement on that. Some would say higher-- maybe 70. Some would say set it to 65. Those are OK. And there are some who incorrectly suggest setting the precharge below 65. If you later find the thermal expansion tank is not empty when you are using a little water, you have a problem.

 

[Sponsor]

 

[bbatl]

While it is the water heater that causes the high pressure, the pressure affects all of your plumbing after the PRV. So I think that the part you put in quotes is inaccurate.

Note that when you are using a little water, the thermal expansion tank should be empty. When you are using a little water somewhere, the water heater expanding water is not a factor. Knock on the tank to learn what empty sounds/feels like. If the PRV regulates to 65 PSI, I would set the air precharge with zero psi water) to 67 PSI. There is not uniform agreement on that. Some would say higher-- maybe 70. Some would say set it to 65. Those are OK. And there are some who incorrectly suggest setting the precharge below 65. If you later find the thermal expansion tank is not empty when you are using a little water, you have a problem.

Thank you. So is there some test I can perform to determine if the high water pressure should be addressed simply by turning the pressure reducing valve counterclockwise or whether the expansion tank needs to be replaced? Thank you.

 

[Reach4]

Note that some of the gauges with the lazy/tattletale hand for recording maximum pressure can give a wrong high recording due to vibration. Tap your gauge to check on that susceptibility.

To check the PRV setting, put the WH on vacation mode (now or before doing the thermal tank stuff) if you have that setting, otherwise turn the WH off. Crack open a faucet. If the water pressure is not 65, turn the adjustment on the PRV until you get 65 steady with the faucet cracked open.

Turn off the water coming into the house. For the pressure tank testing and filling, open a faucet to bring the water pressure to zero. Measure the air pressure at the thermal expansion tank. If it is 30 PSI or more, I would pump it up to 67 with air and turn the water back on. Maybe it was not set right before for some reason. If it is 10 PSI or less, I would replace the expansion tank.

Close the faucet, restore the water, and restore the WH setting.

If you still get a problem after this, it could be that your PRV leaks. It could be that your pressure tank is undersized.

To test for the leaking PRV, when the water pressure is say 72 PSI, put the WH into vacation mode. Do not use any water including icemaker. If the PRV is good, the pressure should slowly drop as the water cools.

 

[Gary Swart]

If the tank is full, when you tap on it there will be a dull thud. If it's empty, it will ring. Expansion tanks are easy to replace. I agree with the above post regarding pressure charging the tank. There is no 100% agreement. I set mine equal to the PRV. Some go slightly higher, some slightly lower. Doubt if there is much, if any, noticeable difference. Expansion tanks have a bladder inside that will fail and require the tank to be replaced.

 

[Jadnashua]

The 'neutral' point on the ET bladder is when the air pressure precharge is equal to the 'normal' water pressure (both are equal when water pressure is applied if the WP exceeds the precharge level, and you can use your air pressure gauge to check your water pressure on the ET). If the ET's precharge is higher than the set WP, the WP will rise to that amount before it can start to compress the bladder. For example, if your nominal PRV setting is 65psi and your ET is set to 72psi...when expansion happens, your WP will rise to 72 before the bladder can start to compress to absorb the water, so your water pressure will not be as stable as you expect. If it is lower than the normal WP, it will decrease how much expansion it can absorb, and it will move further. That flexing is what causes the tank to fail. As long as it's close to the WP, you'd never notice, and the difference in longevity is in the noise, but it should not be much different than your normal WP.

 

[Widgit Maker]

He said we needed to replace the water pressure regulator valve.

Maybe he was right.