CPVC for TPR valve piping

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Austin83

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I live in Texas, and I've got a TPR valve on my hot water heater that is dripping a couple drops every night. It currently has a copper discharge pipe coming off of it. I'm planning on replacing the leaky valve, but I'm not a plumber and I don't sweat pipes. Can I use CPVC for my discharge pipe? I've found some posts where people say no and others say it's okay to use CPVC. Some even suggest it's okay to use CPVC as long as it's not directly connected to the valve. Can I directly attach CPVC to the valve? If not, can I simply use a short brass connection to tie them together? Do I have any other options other than copper (requires sweating) or CPVC that is DIY homeowner simple? Any advice or help is appreciated.
 

Reach4

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I live in Texas, and I've got a TPR valve on my hot water heater that is dripping a couple drops every night.
You should probably have a thermal expansion tank. Typically this dripping occurs when there is a check valve, possibly as part of the water meter, or there is a PRV (pressure reducing valve). Hot water use causes colder water into the water heater. Heater heats and expands the water. Water cannot expand, so the pressures rise to 150 PSI or more and the relief valve lets water out. A thermal expansion tank absorbs the extra water and pressures stay normal.

I use CPVC for my discharge pipe?
Not permitted. Would probably work OK. This is the job where galvanized shines IMHO.
 

Austin83

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You should probably have a thermal expansion tank. Typically this dripping occurs when there is a check valve, possibly as part of the water meter, or there is a PRV (pressure reducing valve). Hot water use causes colder water into the water heater. Heater heats and expands the water. Water cannot expand, so the pressures rise to 150 PSI or more and the relief valve lets water out. A thermal expansion tank absorbs the extra water and pressures stay normal.


Not permitted. Would probably work OK. This is the job where galvanized shines IMHO.

I've got an expansion tank due to a pressure regulator. Sorry, should have stated that.
 

Reach4

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Expansion tank has probably failed.

Turn off the water and open a faucet to reduce the water pressure to zero. Check the air pressure in the expansion tank. It should be at the regulated water pressure or a little over. If water comes out or it will not hold pressure, replace the expansion tank; it has failed.
 

Austin83

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Expansion tank has probably failed.

Turn off the water and open a faucet to reduce the water pressure to zero. Check the air pressure in the expansion tank. It should be at the regulated water pressure or a little over. If water comes out or it will not hold pressure, replace the expansion tank; it has failed.

Expansion tank is okay. It was about 4 or 5 psi under what it's supposed to have, and I check its pressure annually. Is it safe to assume the TPR valve just needs to be replaced?
 

Reach4

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The tank could be undersized. If the valve were bad, I would expect it to dribble more continually than only after you use a fair amount hot water and then stop opening faucets for a while.

http://www.amtrol.com/support/therm_res_sizing.html is one simple calculator. It only looks at 3 factors. The hotter your water heater heats, and the bigger your hot water heater is, the bigger your expansion tank should be.

I would boost the pre-charge to maybe 5 PSI above your regulated pressure. That may be enough to make the difference. Why above?

  1. Won't hurt-- water pressure would still stay below 81 PSI.
  2. Water pressure gauge and air pressure gauge may differ a tad.
  3. Pressure regulator could conceivably vary its regulation pressure a bit with temperature or some unknown factor.
  4. PRV might close tighter if the output pressure is a bit above the setpoint.
  5. Can give a time margin if tank loses air very slowly.
 

Austin83

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The tank could be undersized. If the valve were bad, I would expect it to dribble more continually than only after you use a fair amount hot water and then stop opening faucets for a while.

http://www.amtrol.com/support/therm_res_sizing.html is one simple calculator. It only looks at 3 factors. The hotter your water heater heats, and the bigger your hot water heater is, the bigger your expansion tank should be.

I would boost the pre-charge to maybe 5 PSI above your regulated pressure. That may be enough to make the difference. Why above?

  1. Won't hurt-- water pressure would still stay below 81 PSI.
  2. Water pressure gauge and air pressure gauge may differ a tad.
  3. Pressure regulator could conceivably vary its regulation pressure a bit with temperature or some unknown factor.
  4. PRV might close tighter if the output pressure is a bit above the setpoint.
  5. Can give a time margin if tank loses air very slowly.

Thanks for he suggestions, I've confirmed on the Watts site and Amtrol that my expansion tank is well over the size required. I've got two 40 gallon hot water heaters set at 130* with an incoming pressure of about 58 psi. I will add air to the expansion tank and monitor the leaky valve. What's the consensus on the CPVC discharge line?
 

Austin83

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Can I just use galvanized steel piping screwed into the valve, or even a copper type compression fitting?
 
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