Code requires that if the pressure exceeds 80psi or is likely to exceed 80psi even intermittently we are required to install a PRV (Pressure Reducing Valve) on the main water inlet line and an expansion tank in the near proximity of the water heater.

First thing I'm wondering is if that reading is correct. 150psi inside a house is HUGE. Can hardly believe you haven't seen something bad happening because of it already.

Assuming it is accurate and assuming you're on city water, you will want a PRV (pressure-reducing valve) installed immediately downstream of your meter. If this is city water and that's your street pressure, I strongly suspect there is already a PRV installed and it has failed. Either way, you'll want to fix it pronto.

This will also "close" your system so you will want an expansion-tank next to your water heater to avoid pressure-spikes. This has been well-covered recently in posts by justalurker if you want to look it up.

If you're on well-supply, it's a whole different deal. Please advise.

I am on city water and we have a pressure control valve which limits the pressure coming into our unit. I also have a pressure relief tank by the water heater and that is where I have a water pressure gauge. and it retains the maximum pressure recorded. When I look the current water pressure is always around 50-54 PSI and today when I looked it had reached 140 PSI since I last reset it.

Uncle Dewey

Then your thermal expansion tank has probably failed. Usually results is a ruptured membrane in the tank. You can check by pushing the air valve on the thermal expansion tank. If you get sprayed by water then the membrane has failed cause there should only be air in there.

I checked and no water came out of the air valve. Could that mean there is too much air pressure between the membrane and the metal part of the tank? Maybe I should remove all of the air through the air valve?

Thanks heaps for your interest. Uncle Dewey

As far as I know the only way to get a spike in a closed plumbing system that has an expansion tank is for the connection to the thermal expansion tank to be blocked effectively taking the tank out of the system or for the tank to have failed. Working properly a thermal expansion tank absorbs the spike.

A 150psi spike should trip the T&P valve on the WH.

In order to check the air pressure in the thermal expansion tank it needs to be empty of water. Here are the installation instruction in PDF form for a thermal expansion tank and it details how to set the pressure... http://media.wattswater.com/2915054.pdf

If you can't find the problem get a licensed plumber in there right away. Those spikes may take out your WH but more important, if the T&P valve on the WH fails bad things can happen.

Hi Again,

I now know how to check with no water pressure, but I'm not sure what pressure I should set the expansion tank at no water pressure.?

Uncle Dewey

Read the installation instructions at the link two posts up... that's why I posted the link.

That's what happens when dealing with a neophyte. I have read the instructions so I know I have to remove all water pressue, but the instructions are first of all for a new installation, but even then leaves me with what pressure should be on the outside of the bladder under no water pressure. Maybe it is plain to others, but not to me.

Uncle Dewey

The following italics are word for word from the installation instructions...

Installation
1. Before beginning installation determine the system pressure.
a. Open a faucet to allow the system pressure to equalize.
b. Close faucet.
c. Read the system pressure at the pressure gauge (Figure 1).
2. The expansion tank pre-charge must be set to the system pressure as
determined in Step 1. Pre-charge prior to installation in the system.
Caution: Pre-charge prior to installation in the system.
Do not adjust the air pre-charge of the expansion tank
with the system under pressure. The air pre-charge
should only be adjusted under zero system pressure.
Note: The normal pre-charge is 20psi (138 kPa).
Do not exceed 80psi. If system pressure exceeds
80psi (5.5 bar) it will be necessary to either: A. Add a
pressure reducing valve to the system or, B. Locate the
expansion tank in a riser where the static pressure is
below 80psi (5.5 bar).
a. Unscrew the protective cap from the air inlet valve.
b. Using a tire pressure gauge, check the tank pre-charge pressure.
c. If necessary, pressurize the tank to the proper setting using a manual
bicycle tire pump. Caution do not exceed 80psi.
d. Replace the protective air cap.

So, since you've already said your static water pressure is 50-54 psi we'll use 55 psi as static pressure (54 psi is high pressure but 55 is just an EZ number to remember).

You set the air charge in the tank to 55 psi with the tank empty. Use a bicycle pump cause a compressor can rupture the bladder.

Then you reinstall the tank and turn the water on and then open a faucet to let the air in the water side of the tank come out.

If the tattletale needle on the pressure gauge stills shows 140 psi spikes GET A PLUMBER NOW.

Ya know, there's no shame in hiring somebody to do stuff you can't figure out. For heaven's sake, this is important. If you don't get it, bring somebody in who does. Needs to be right and YOU need to have peace of mind about it being right before you leave it alone.