I am completely stumped. You guys helped me out a lot with my previous question here: What could be causing water to drip from the relief valve of my new gas water heater?

Turns out the expansion tank bladder was filled with water and needed to be replaced. I got a new 2 gallon 100 psi max expansion tank but before putting it on I measured the water pressure at around 100 psi which seemed awfully high to me. When I turned a faucet on the pressure would drop to around 50 psi and I would get a steady stream of moderate pressure. It seemed to steady at around 68 psi so I used that as a good starting point.

Instructions that came with the tank said to install at 2 psi below normal cutoff pressure. Thinking that was awfully specific, I set the air pressure in the new tank to 65 psi and installed it.

I ran the faucets a LOT to make sure I got all the air pockets out but now I notice bizarre fluctuations in my water pressure for the past few days. I have normal water pressure in the basement, acceptable water pressure on the first floor, and virtually NO pressure at all on the upstairs floor, where this was never a problem before.

Leaving the gauge on downstairs the pressure would slowly continue to rise as high as 100 psi at times EVEN AFTER seriously turning the pressure regulator back. When I turn the water on I get a good stream of water then 5 seconds later nothing but a trickle as the water pressure only reads 20 psi when the water is running.

So now I only see four possibilities:

  1. The gauge is broke, there is no flippin way that I have my pressure regulator turned back that far and actually have 100psi build up in the pipes all the way from 20 psi.

  2. The pressure regulator is broke, it is extremely old looking and doesn't have a PSI reading on it, just a hex bolt head that when turned out will decrease the pressure.

  3. The new expansion tank is defective and slowly leaking air into the system causing me to have almost no pressure upstairs

  4. I set the air pressure too high/low in the new expansion tank and it is causing havoc with my internal pressure.

About the only positive thing I can say about everything is that my safety relief valve on the water heater is no longer leaking water so I must have done something right. Maybe I just need to increase the pressure to the house but if my pressure increases to 100 psi slowly while the water heater runs and I have an expansion tank rated for 100 psi then I am afraid I could be creating a dangerous situation.

Any suggestions? I am going crazy over this and I stink because I can't take a proper shower ;)

3 Answers 3


Sorry to hear about your "odor" problem. Maybe there is a local public fountain you can take a dip into!!!

However, the problems you describe are fairly common, but may be tricky to isolate. Let's try some basics: Relieve the pressure from the bladder completely. Let the well pump fill the tank completely and bleed any air from the system using the faucets with the pump running. Again, with the tank full of water, close all outlets and charge up the bladder to about 60PSI. Most systems work fine between 45 to 65 PSI. Anything over 70 is pushing it. The tank needs to be charged when full, not empty. Monitor the pressure as you draw water. Does the pump kick on constantly when the pressure reaches the low limit, and off at the high limit? This will help tell if the regulator is working properly.

Is there any pulsating water pressure at the faucets?

When you are sure you have a full tank, no air in the system, is your second floor water flow ample when the tank is reading 60psi?

There are a few "if's" here. Depending on how the pump behaves and the pressure responds, you have to determine if the problem is with the pump and volume of water being delivered to the tank, or if the pressure regulator is properly operating.

If you are still seeing any pulsating water pressure at the taps, then the bladder is water logged again. If the bladder pressure drops too quickly, then most likely the volume of water from the pump is low. The pressure should remain fairly constant at the tank if all the functions of the pump and regulator are working properly. Good Luck

  • I missed the well pump, assumed the PRV indicated high pressure from the municipality. You're thinking otherwise? +1 for the public fountain shower! :)
    – BMitch
    Commented Jun 10, 2012 at 11:46
  • Usually public water supplies run at around 70psi and don't require an additional pressure tank. I have never seen a tank used in a small residential home with public water unless in a very low pressure area which would be very uncommon and require completely different regulation as there is no "on/off" like with a well pump. Commented Jun 10, 2012 at 11:56
  • I may be misunderstanding his problem. maybe he is talking about a small pressure tank off a furnace slaved to hot water only????? Commented Jun 10, 2012 at 11:59
  • @shirlockhomes Thanks but it is municipal water. It is coming from outside at a high pressure which is why the water authority insists that all homes have a regulator. It is a 2 gallon expansion tank on the cold line so increased water pressure from the water heater doesn't damage fixtures in the home. Commented Jun 10, 2012 at 12:01
  • 1
    My municipal water has high pressure. And either my PRV or the city's meter has a backflow preventer, so when the hot water tank heats up, the pressure jumps in my home.
    – BMitch
    Commented Jun 10, 2012 at 12:01

If you're seeing it climb to 100psi while the water heater isn't running, then the pressure regulator is broken.

If it's climbing to 100psi while the water heater is running but stays at normal levels all other times, the expansion tank isn't working. Maybe it's defective, or maybe it's not installed properly. It's also possible the tank is undersized for your hot water heater.

If you have full pressure upstairs, but just not enough flow, then you may have a blockage in your pipes. A common place to check for blockages are valves that you hadn't used in a long time but recently shutoff and reopened and aerators or filters in the fixtures. I'd also take a 5 gallon bucket, place it under your best faucet, and see how fast you can fill it. Then compare that time to how long it takes to do the same at your neighbor's home. Use process of elimination to track down any blockage. If it's every faucet, then you probably have a problem on your main line. If it's only one fixture, then check it's valves, aerator, and any filter.

  • How do I tell if I have normal pressure small flow? I am guessing it is both low pressure and low flow. Good lord I hope it is not a blockage somewhere, how would I even go about finding a problem like that?! Commented Jun 10, 2012 at 12:04
  • You'd need to get that pressure gauge on one of the high fixtures. You may be able to get a piece of flex hose and an adapter to connect at the shutoff valve under the sink or toilet.
    – BMitch
    Commented Jun 10, 2012 at 12:07
  • One tell tale sign of high pressure is a difficult to open valve or a sudden burst when you first open the fixture. I'd also keep an eye out for leaking toilets.
    – BMitch
    Commented Jun 10, 2012 at 12:08
  • Then it is high pressure then because I have both sudden burst and leaking toilets. That means when I installed the expansion tank I must have introduced something that blocked the flow. Any tips on how to locate the blockage? Commented Jun 10, 2012 at 12:23
  • @maple_shaft Any shutoff valves that hadn't been used in a long time before your repair are the first suspect. The washers inside tend to degrade over time and either don't close all the way or fall apart when reopened. If you've been adjusting the PRV, it's also possible something in there has broken. But for an easy test, try removing the aerator on the sink to make sure you didn't knock a bunch of sediment loose.
    – BMitch
    Commented Jun 10, 2012 at 12:28

Municipal Water systems require a Pressure Reducing Valve (PRV).

It is not recommended to have the house psi above 90. 70 is the norm in most municipal systems. An expansion tank is needed if there is a check valve installed on the in line. If there is a water meter, there is an excellent chance of one being installed. Many water utilities mandate check valves, or also known as RPZ's on their systems, also.

An expansion tank is needed after the meter/check valve. This is due to the expansion of water in the heater (or boiler). If the water pressure drops considerably while running a faucet, it is probably due to a faulty PRV. Adjusting the PRV by turning the adj. screw counterclockwise reduces the psi. Clockwise increases the pressure. (most PRV's). If the pressure is too high, it can wreck even a new expansion tank. Too low of psi, and the bladder will never "squish" to take up expansion. The psi on the in line psi after the PRV, and the precharge on the expansion tank should be the same.

1st step. Check gage after PRV for static water psi read. (nothing running) If the psi is higher than 70, adjust it. Run the water and then turn it off, and read the gage. Repeat as necessary. If the proper static psi cannot be achieved (by staying where you had it reading, and not climbing), then condemn and replace the PRV.

2nd step - install a precharged to house psi expansion tank. Run the water and observe. There will be a psi drop as water runs. It should not be a large drop. That would mean a partially closed valve somewhere or an obstruction. When the water is off, the psi should only return to the set 70 psi. Not climb higher. Again, that means a defective PRV. Hope the class helps.

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