Help! High water pressure even after installing a thermal expantion tank.

[byoder7]

I recently purchased a home and within the first two weeks a valve broke under the master bath sink. It leaked into ceiling below, bummer!! I suspect high water pressure caused the leak. I measured the pressure at 110 PSI - pretty high. I suspected the issue was the PRV (pressure regulating valve) had gone bad, so replaced it for about $1,000 (I know it's a ripoff). And made sure that my pressure stayed at the 55 PSI the PRV was set at.

But when I checked the pressure first thing in the morning it had jumped to 104 PSI! After doing a bunch of research I figured out that most likely cause was I needed a thermal expantion tank for the hot water heater. So I purchased and installed a WATTS PLT-12, and it is now installed. My baseline water pressure is 55 PSI, but now when I wake up the pressure still goes to 85 PSI, which I still feel is high. I was under the impression that the thermal expantion tank would ensure the pressure stays almost exactly at 55 PSI. I have replaced the thermal expantion tank twice, so I know that it is not broken, and it is precharged to 55 PSI as it should be.

My specs:

- PRV (pressure reducing valve) set to 55 PSI.

- WATTS PLT-12 thermal expantion tank installed on a "T" off the cold water line to the water heater. And this is "pre-charged" to 55 PSI.

- New GE 48 Gal NOx water heater.

- House built in 1997

 

[phishfood]

Try shutting the power off to the water heater before you go to sleep, and see if the pressure has increased in the morning. If it has, I would suspect that your PRV is leaking by.

 

[speedbump]

Any bladder tank should be set lower than the pressure in your plumbing or it can't take in any water unless the pressure goes higher than the 55 psi.

 

[byoder7]

I am going to go one day without the hot water heater running to ensure the PRV is working OK and rule that out. I watched the video below (from Watts on YouTube) on how to adjust the precharge pressure, and they are saying to set it at the same pressure as your static (baseline) water pressure (see link below).

[ame=http://www.youtube.com/watch?v=MT1MTEZREQk]YouTube - Adjusting the Pre-Charge of a Thermal Expansion Tank[/ame]

I think the issue would be if you have LESS\LOWER pressure in the thermal expantion tank then it is going to be always full of SOME water (since if the pressure is lower than your static water pressure than water will want to flow into the thermal expantion tank to equalize). And thus you would have less ability to absorb the thermal expansion. For example if I understand it correctly if the pressure in the thermal expansion tank was set at 60 PSI, and the static water pressure was 55 PSI then you may see the pressure rise to 60 PSI when the water heater cycles. But it should not go much higher than that, since the thermal expansion tank SHOULD absorb anything higher than that.

If you did the oposite, say set the thermal expansion tank at 55 PSI and water pressure at 60 PSI then as soon as you hook it into your system water will flow into the thermal expansion tank (since it is at lower pressure) - which will cause it to work less eficiently. Granted that as water flows into the thermal expantion tank I assume that the air pressure in it will build (since the air is getting compressed as water flows into it), however it should be minimal and I am not sure what the specs are on that.

So can we confirm the "best practice" is to set the thermal expantion tank as close as possible to your static water pressure (i.e. the same setting as the PRV)? Thanks everybody!

 

[byoder7]

After my test (turning water heater off for the day) my PSI stayed at 55 PSI. So the PRV (pressure regulating valve) is working.

Now I am out of ideas. It seems that the thermal expansion tank is not working 100% correctly - or the hot water heater is defective and somehow it is expanding way beyond the norm.

Again the thermal expansion unit is installed upside down (which I read is OK) above the water heater, and is attached via 18 inch hose to a 3/4" T off the "cold" water line. The other ends of the T go to the wall "cold" water pipe, and to the water heater.

One more thing to consider: It seemed strange that when the water was turned off (and nothing was hooked up to pipes coming out of wall where water heater goes) water flowed out of both "hot" and "cold" pipes. Not sure what that means, but maybe it's related.

I have attached diagram of my setup.

 

[speedbump]

Apparently the dude with the two gauges and the tire pump has never seen a bladder get stuck to the bottom of the tank.

 

[byoder7]

You may be right! So in my case with 55 PSI base water pressure (PRV is set to 55 PSI) what would you suggest I set the thermal expansion tank pre-charge to? Like 50 PSI or even lower?

 

[speedbump]

If your system stays at 55, then just a few pounds below that would be fine. This way, the bladder is held up off the bottom and there is still plenty of space for the expansion of heated water. That tank will hold about a gallon of water before you start stretching the bladder. If you stretch it too much, it will tear and that will be the end of it. I don't know how much water can expand from heat, but I would think a gallon in a normal plumbing system would be a LOT.