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Old 04-14-2013, 08:26 PM   #16
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My pressure relief valve is hot to the touch


blow off the relief let it flush the seat up pin flushes back down closes relief...

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Old 04-14-2013, 10:37 PM   #17
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My pressure relief valve is hot to the touch


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Originally Posted by jagans View Post
Thank You Daniel, as always, an intelligent, thoughtful answer. I have asked a gazillion times on this forum if my well water expansion tank would serve as expansion for my HWH as it simply made sense that it would since it is in series with the HWH and there is no check valve in the line between the two. You have answered the gazillion and first request.

Your well tank will not meet the IPC because it is not a hot water expansion tank. So I would turn it down.
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Old 04-15-2013, 03:13 AM   #18
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My pressure relief valve is hot to the touch


You may find that after adding an expansion tank you may need to replace the TPR valve depending on how lomg it was leaking.

I had a similar problem where I had an expansion tank that was no longer working and the TPR kept opening. Finally I replaced the expansion tank and found that my TPR had accumalated alot of scale from the constant flowing water and would not seat itself closed properly. I probably coulld have soaked it in some CLR or something but for the cost and the piece of mind, I just replaced it with a matching spec new one.
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Old 04-15-2013, 09:01 AM   #19
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My pressure relief valve is hot to the touch


According to the sticker on the tank you installed it about 3mo ago. Is that accurate? If so, has it been fine for those 3mo up until now?

I feel like we don't know enough about your system to make a diagnosis yet. Do you know if you have a PRV? (pressure reducing valve) I recently replaced our WH and it was also leaking from the TP valve right off the bat. Turns out our PRV was bad and we have extremely high water pressure living downtown in the city so we were getting nearly 160psi, which was enough to spray out the TP valve.

Do you know what your water pressure is? I suggest you go to lowes/hd and get a pressure gauge w/ a female hose thread. ($10-15) It should have a black dial to actively measure the pressure and a red dial to mark your highest reached pressure. Then install it at the bottom of your tank on the plastic drain valve. Once you have it hand tight give it another 1/2 turn w/ a wrench. Then get a flathead screwdriver and open the valve. You should get a reading immediately. If it's in a normal range (50-60psi) then leave it alone for a day and come back to see where your red dial is. We want to see if it reached the 150psi level which is where it should need to be to open your TP valve.

Let us know what you find from doing this test and myself or the others will be able to give you some useful info.




EDIT: jagans I too am a bit puzzled by the requirements for the thermal expansion tank, mainly because I don't know exactly how much of a psi increase occurs when the water is heated. Ghost, nice post w/ good reasons. The warranty, insurance and code requirements I understand. What I don't exactly understand is how much of an increase we're dealing with in the 'average' house.

Let's say the average house has a 40 or 50gal tank water heater. Let's say their water pressure is between 50-60psi. (I know some are much higher but given the right circumstances with a PRV in place it should be in that range) Incoming water temp ranges depend on where you live, can be in the 70's in Florida or in the 30's in North Dakota - where I live it's around 50F. So let's take the worst average case of thermal expansion, which would be a 50gal tank @ 60psi with 35F incoming water temp. What I'd like to know is how much the pressure will increase in the tank when this volume of water is heated to say 120F?

I always see people saying "oh, you're TP valve's spraying, you need a thermal expansion tank" but I've never actually seen it justified. Would the above 'worst case average scenario' create a pressure rise of 90psi, which is what it would take to hit 150psi and kick open the TP valve? I've googled this topic before to try and figure it out but honestly it seems very complicated. I have found some info here and there stating the average pressure increase in a 40gal tank is only about 10-15psi once the water is heated. If this is true, then people need to stop using this rational. Yes the person might need a thermal expansion tank, but let's not tell them the wrong reasons, let's tell them the actual reasons - warranties, insurance, code, etc.

Any scientific/mathematic brains want to chime in with an answer, you would be my hero.

Last edited by fetzer85; 04-15-2013 at 01:40 PM.
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Old 04-15-2013, 03:01 PM   #20
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My pressure relief valve is hot to the touch


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Originally Posted by Daniel Holzman View Post
That is a TPR valve for a hot water tank. As noted previously by several posters, your system requires a means of relieving pressure as the water heats up. If you are on a well, you typically have an expansion tank for the well pressure, which doubles to allow pressure relief for hot water. If you are on city water, as previously noted, if you DO NOT have a pressure reducing valve or a backflow preventer, the city mains act to relieve excess pressure. If you have either of those devices, you need an expansion tank.

You may have an expansion tank that is no longer functioning. Malfunctioning expansion tanks have been discussed many times on this forum, if you think you have an expansion tank that may bad, search on this forum for discussions about testing and repairing expansion tanks.
Where would I find a pressure reducing valve or a backflow preventer?
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Old 04-15-2013, 03:09 PM   #21
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My pressure relief valve is hot to the touch


"According to the sticker on the tank you installed it about 3mo ago. Is that accurate? If so, has it been fine for those 3mo up until now?"
Yes it was installed according to the date on the sticker. It didn't leak for about the first week or so and since then is has leaked and seems to be getting worse. Originally I only had to empty the bucket once a day and now it is up to twice almost 3 times per day. I recently turned down the temp on the heater to see if that would help but it has only been one day since I did that so I am waiting to see if it had any effect.

"Do you know if you have a PRV? (pressure reducing valve)"
No I do not know if I have a PRV. Where would it be and what would it look like?

"Do you know what your water pressure is?"
I do not know what my water pressure is but following your post I will find out as soon as I can.


Many thanks to everyone for their input. I am learning much and I hope to learn more and fix my problem. Again, THANKS!!
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Old 04-15-2013, 03:10 PM   #22
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My pressure relief valve is hot to the touch


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Originally Posted by biggles View Post
blow off the relief let it flush the seat up pin flushes back down closes relief...
What do you mean by this?

Thanks!
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Old 04-15-2013, 03:52 PM   #23
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My pressure relief valve is hot to the touch


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Where would I find a pressure reducing valve or a backflow preventer?


Lowes, HD...most home improvement / plumbing supply places.
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Old 04-15-2013, 05:43 PM   #24
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My pressure relief valve is hot to the touch


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No I do not know if I have a PRV. Where would it be and what would it look like?
It should be fairly close to your water meter. Here's a pic of mine, if you have one it should look similar.
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Old 04-15-2013, 06:41 PM   #25
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My pressure relief valve is hot to the touch


For Fetzer
Computing the increase in pressure due to a change in temperature in a completely full, sealed container that is assumed to NOT expand is done in the following way.

First, the temperature coefficient for pure water is .000207 per degree Celsius. For a temperature rise of 30 degrees C (54 degree F) the water will expand by .0062 times the original volume of water, or approximately 0.6% expansion. Therefore, your 50 gallons of water will expand to 50.31 gallons when heated in an open container.

We assume that we do NOT have an open container, in fact we assume that the water is sealed, because there is no expansion tank, and no air in the system. To compute the change in water pressure for such a situation, we use the bulk modulus of water, which is 2.2x10^9 pascal, or 319,000 psi. The bulk modulus of water equation is:

deltaP = (K/V) * deltaV

where deltaP is the change in pressure, K is the bulk modulus of water, V is the initial volume of water, and deltaV is the change in the volume of water that would occur if the water were allowed to expand due to the temperature change.

In English, this means that to compute the pressure change in psi, we multiply the modulus K by the change in the volume of water, and divide by the initial volume of water. In our case, the initial volume is 50 gallons, the change in volume that would have occurred if the container were open is 0.31 gallons, so the change in pressure would be 319,000 * .31 / 50 = 2,000 psi.

Of course, you would never see a rise of 2,000 psi in any real system, even one with no expansion tank, since the thin copper pipes would expand, the water tank would expand, and there is always some air in the system to absorb some of the pressure. But you get the idea, a change in temperature that results in a relatively small volume change can produce a very large pressure change in water. And that is why there is an expansion tank, which in practice need only absorb less than a gallon of expansion for a 50 gallon tank.
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Old 04-15-2013, 06:47 PM   #26
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My pressure relief valve is hot to the touch


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Originally Posted by fetzer85 View Post
According to the sticker on the tank you installed it about 3mo ago. Is that accurate? If so, has it been fine for those 3mo up until now?

I feel like we don't know enough about your system to make a diagnosis yet. Do you know if you have a PRV? (pressure reducing valve) I recently replaced our WH and it was also leaking from the TP valve right off the bat. Turns out our PRV was bad and we have extremely high water pressure living downtown in the city so we were getting nearly 160psi, which was enough to spray out the TP valve.

Do you know what your water pressure is? I suggest you go to lowes/hd and get a pressure gauge w/ a female hose thread. ($10-15) It should have a black dial to actively measure the pressure and a red dial to mark your highest reached pressure. Then install it at the bottom of your tank on the plastic drain valve. Once you have it hand tight give it another 1/2 turn w/ a wrench. Then get a flathead screwdriver and open the valve. You should get a reading immediately. If it's in a normal range (50-60psi) then leave it alone for a day and come back to see where your red dial is. We want to see if it reached the 150psi level which is where it should need to be to open your TP valve.

Let us know what you find from doing this test and myself or the others will be able to give you some useful info.




EDIT: jagans I too am a bit puzzled by the requirements for the thermal expansion tank, mainly because I don't know exactly how much of a psi increase occurs when the water is heated. Ghost, nice post w/ good reasons. The warranty, insurance and code requirements I understand. What I don't exactly understand is how much of an increase we're dealing with in the 'average' house.

Let's say the average house has a 40 or 50gal tank water heater. Let's say their water pressure is between 50-60psi. (I know some are much higher but given the right circumstances with a PRV in place it should be in that range) Incoming water temp ranges depend on where you live, can be in the 70's in Florida or in the 30's in North Dakota - where I live it's around 50F. So let's take the worst average case of thermal expansion, which would be a 50gal tank @ 60psi with 35F incoming water temp. What I'd like to know is how much the pressure will increase in the tank when this volume of water is heated to say 120F?

I always see people saying "oh, you're TP valve's spraying, you need a thermal expansion tank" but I've never actually seen it justified. Would the above 'worst case average scenario' create a pressure rise of 90psi, which is what it would take to hit 150psi and kick open the TP valve? I've googled this topic before to try and figure it out but honestly it seems very complicated. I have found some info here and there stating the average pressure increase in a 40gal tank is only about 10-15psi once the water is heated. If this is true, then people need to stop using this rational. Yes the person might need a thermal expansion tank, but let's not tell them the wrong reasons, let's tell them the actual reasons - warranties, insurance, code, etc.

Any scientific/mathematic brains want to chime in with an answer, you would be my hero.
Only takes 150 PSI to make it drip.... I have seen it to many times to count. A hot water pressure expansion tank takes care of it. About 42 Dollars US
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Old 04-15-2013, 06:48 PM   #27
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My pressure relief valve is hot to the touch


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Originally Posted by tntlassiter View Post
Where would I find a pressure reducing valve or a backflow preventer?
If you are on city water, follow your main water line coming into house from your water meter. PRV's come with a backflow preventer in them. Your water meter may also have a backflow preventer as well. You can ask your municipal water department. If you are on well, follow your main coming from well. Fetzer85 posted a nice pic of one.

A plain backflow preventer, will look like a 3 inch or so round long valve with unions on both ends. Sometimes they are installed on incoming water lines leading to boiler/hwh. I'm on cell phone now with no access to internet i'll post a pic later if some else doesn't frist, of what it looks like.

If you find something and you don't know what it is, post a pic of it and we will tell you what you got. Thanks.

Last edited by jmon; 04-15-2013 at 06:54 PM.
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Old 04-15-2013, 09:26 PM   #28
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My pressure relief valve is hot to the touch


Daniel, thanks for the step-by-step details. Very interesting.

Ghost, I guess I just didn't think heating that volume of water would create a 90+psi increase, but based off Daniels explanation its more than possible.

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