Our contractor installed a pressure regulator because pressure was too high on the side of the house where we remodeled bathrooms. I measured pressure and it was around 78 but after using cold water only, the pressure spiked to 108 and remained for several days until I released water from the hose bib outside. We refrained from using any hot water. Then I measured the pressure and it was 80, then ran cold water and it spiked to 108 until releasing water from the hose bib. We don’t have an expansion tank on the water heater but why would the pressure spike to over 100 immediately after using cold water only?

  • 1
    Pressure regulator is defective or installed wrong. Or needs to be adjusted down. Plumbing should be 80# or lower. Lower is better. An expansion tank might help, but plumbing joints do not like spikes, and you do not like them inside of walls. Adjusting down to 60# would be better.
    – crip659
    Commented Mar 20 at 22:38
  • what type/model is the pressure regulator ?
    – Traveler
    Commented Mar 20 at 23:05
  • Thank you for your responses-much appreciated. It was initially set at 65, then adjusted down to 60. When the contractor’s plumber was here last, he looked at it but I’m not sure if he made another adjustment. I’m not sure what type of regulator it is but I think it is the one with a spring mechanism. Just seems odd that after I run cold water only and I immediately go out to measure and it spikes to over 100. I too think that it may be defective. Is there a way to see if it was installed wrong or measure differently to see if it is defective.? Thank you!
    – Cewe
    Commented Mar 21 at 0:42

1 Answer 1


It is almsot impossible to install it wrong, but then there are always some who find the way. When you open the faucet the pressure will drop (that is normal) and the regulator compensates by increasing the pressure to the set value.

If you have one of those quarter turn ball valve and closed it rapidly the regulator has no time to react/adjust.

Regulator only works when water is flowing, and does noting when there is no flow.

Before you mess with replacing regulator try following.

Very slowly close the valve and observe the pressure now.

You should do it soon, because the very high pressure can damage your plumbing.

  • Thank you for your input. I think it is doing the opposite of what you indicated but I may be misunderstanding. When I run the cold water from the faucet inside, this is when the pressure spikes to over 100 immediately. It reduces only when I run the outside hose bib.
    – Cewe
    Commented Mar 21 at 1:57
  • The pressure regulator is made to reduce the incoming pressure, not the other way around. It can not increase the pressure over the incoming pressure. If you have a spike when you open a valve then you pressure regulator is installed the wrong way (Opposite). Observe if there are arrow markings on regulator. (like iN/Out)
    – Traveler
    Commented Mar 21 at 2:04
  • Normal water pressure runs between 40 PSI and 60 PSI
    – Traveler
    Commented Mar 21 at 2:26

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