T&P Valve activated

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Dato Da

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Hi,

I had a new power-vented gas water heater installed about two weeks ago. Yesterday I noticed that there' some water on the floor around the heater. From the location of the water (right under the pipe connected to the T&P valve) and the fact that there were some droplets on the side of the tank right at the opening of the pipe, I believe the T&P valve was activated. I dried up the area and it's been dry since.

My question: Should I be concerned that the T&P valve was activated? Just one extra piece of info-- I do have an expansion tank on my cold water line.

Thanks!
 

Reach4

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Yes, be concerned. Here is where you will go next.
  1. Measure the water pressure while trickling water somewhere. A garden hose thread pressure gauge is under $20 and often well under. If over 80 PSI, further action will be needed.
  2. With the water pressure at zero (house water turned off, and open a faucet), the pressure tank should be empty. If you knock on the tank and it does not sound empty, replace the failed pressure tank. Otherwise continue to step 3 with the existing tank.
  3. Set the air precharge in the pressure tank to 1 or 2 PSI higher than what you measured in step 1.
  4. Turn the house water back on.
 

Dato Da

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Thank you guys very much for the helpful replies.

A couple of follow-up questions:
1. Regarding Step 3. Does that mean that I should set the expansion tank to 61 or 62 psi if I measure 60 psi in Step 1? I read somewhere that the expansion tank is usually pre-charged with 12 psi. That's a big gap between 61 psi and 12 psi. Am I missing something really basic here?
2. My water heater was professionally installed. Do I have a case to ask the installer to come back and make the adjustment free of charge? From my very unprofessional perspective, this all seems to be the fine-tuning that the installer should have done when they finished the water heater installation.

Thanks again!
 

Reach4

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Regarding Step 3. Does that mean that I should set the expansion tank to 61 or 62 psi if I measure 60 psi in Step 1? I read somewhere that the expansion tank is usually pre-charged with 12 psi. That's a big gap between 61 psi and 12 psi. Am I missing something really basic here?
That was for a heating boiler.

There are some reasonable differing opinions on the right air precharge for an expansion tank. But they all put the desired precharge close to the normal water pressure. If your water pressure was 60 and the precharge was 70 or 59, you would probably be OK too.

The actual ideal would be around the highest water pressure that the city delivers. That is often higher in the middle of the night. There are often differences in the calibration of your water pressure gauge and your air pressure gauge. So I think air 2 psi is on balance near ideal for the real world.

My water heater was professionally installed. Do I have a case to ask the installer to come back and make the adjustment free of charge? From my very unprofessional perspective, this all seems to be the fine-tuning that the installer should have done when they finished the water heater installation.
I don't know. Your tank could be undersized too. There are charts and calculators. Adding air yourself is not hard. But if the unit is undersized, unless you selected the size .... What brand and model of expansion tank did you get?
 

Jadnashua

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A hydronic ET is often around 12psi because that's a common pressure for use with a boiler.

Some ETs can work on either hydronic or potable water, some use different materials, and will only work on the system designed for it. A potable water one often would come precharged to 40psi. But, to reach their design capacity, the bladder needs to be at it's equilibrium point so it can accept the maximum volume without being stretched too far, and that means, it should be very near the static water pressure. If the water pressure is 60psi, and the air pressure is 60psi, the bladder is not being stretched or compressed and it will last longer. The T&P valve will open for one of two reasons: over pressure (typically 150psi) or over temperature (typically about 210-degrees F). IF that safety valve opens for some other reason, it's defective. If it's doing its job, keep in mind that they aren't designed to open/close frequently...that can cause mineral deposits that can freeze it up long-term. Plus, the water draining can cause damage, depending on where it discharges.
 
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