# T and P Valve on water heater



## Bacchus208 (Jan 5, 2014)

I have often trained my guys how to diagnose why a T+P is leaking on a water heater. The for reasons I have found have been 
1) The temp is turned up to high
2) The thermo expansion tank is bad
3) The T&P has a weak spring or trash jammed in it
4) Presure in the house is inconstant caused by a bad PRV

Can anyone else think of possible reasons the T and P could be leaking?


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## ROCKSTARPLUMBER (Dec 14, 2008)

Hard water.


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## gassyplumber (May 1, 2011)

Could be that someone took a lot of short draws of hot water and caused the water to stratify. Cold at aqua stat but screaming hot on top


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## Coolcanuck (Jan 30, 2012)

Worked for a very large company that had rental tanks, first good outside temperature drop every fall was guaranteed t&p valves and tank blow outs. Million and a half customers and its something I prepare for every year now.


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## Dpeckplb (Sep 20, 2013)

Here it is because with a check valve at the meter which makes it a closed system, the pressure has no where to go therefor tripping the t and p valve. To rectify this we were instructed by inspectors and bradford white to install a expansion tank. 
I also have been told by the supplier that the t and p valves have been manufactured with weak springs. The suppliers were not to tell us plumbers. Any ways I hope this gives you some insight, or at least my opinion.
Cheers


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## MTDUNN (Oct 9, 2011)

T&P stands for temperature and pressure. We first need to understand how a water heater's temperature and pressure gets too high. 

One example is too many people in the house. Think about it. If a migrant family moves into a home for the grape season in wine country, this can cause that T&P valve to start dripping. And here's how.

Papa wakes up first and slaps Momma on the butt cheeks and tells her to start the coffee while he takes a hot shower, Momma then wakes up her 2 brothers, 4 daughters and their spouses and Grandpa. Thankfully there is another bathroom in the migrant house in the vineyard and the family starts taking their showers one at a time. By the time they all take showers, momma is stuck with a cold shower after making coffee for 13 grape pickers. She yells at Papa "no hot water!" So Papa raises the temperature for hotter water. 

Then their kids wake up, all 23 of them. Papa tells them to only take a 2 minute shower and 2 at a time. But it's still too cold and Papa turns it all the way up. 

The next morning Papa notices a leak coming from the T&P valve after everyone took their morning showers. He puts a bucket under it to catch the water. And decides to fix it later because they need to get out to the grape field to water down the dirt to keep the dust down while picking grapes for that fine Pinot Noir. 

But there is not enough water pressure to hose down the dirt because all the kids are taking showers. And Mama will take all day to wash clothes and dishes. So the next day Papa buys a booster pump and connects it to a hose bib on the migrant house. Now there is enough water pressure to water down the field and wash dishes. But Papa notices that the bucket it filling faster and has an idea. He buys a plug to stop that pesky leak. 

But tragedy. During the night while they where sleeping, the water heater blows up. The vineyard and the migrant home catches on fire and a whole generation of migrant workers are burned to death from that explosion.

This saddens the owner of the vineyard greatly because there be no fine Pinot Noir this year.


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## Redwood (Sep 8, 2008)

Dpeckplb said:


> I also have been told by the supplier that the t and p valves have been manufactured with weak springs. The suppliers were not to tell us plumbers.


That is by design...
Those springs are designed to allow the valve to open at the rated pressure of the valve, and they actually are quite precise...


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## MTDUNN (Oct 9, 2011)

Redwood said:


> That is by design... Those springs are designed to allow the valve to open at the rated pressure of the valve, and they actually are quite precise...


 Or that too but I like stories


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## rjbphd (Feb 5, 2010)

Bacchus208 said:


> I have often trained my guys how to diagnose why a T+P is leaking on a water heater. The for reasons I have found have been
> 1) The temp is turned up to high
> 2) The thermo expansion tank is bad
> 3) The T&P has a weak spring or trash jammed in it
> ...


Wow.. already posting here and whoring this site without doing the proper introduction as per request..


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## MTDUNN (Oct 9, 2011)

rjbphd said:


> Wow.. already posting here and whoring this site without doing the proper introduction as per request..


Did you apply for a job?


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## MTDUNN (Oct 9, 2011)

Because if not. I know a winemaker looking for grape pickers


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## buddy72 (Dec 16, 2013)

Great story mtdunn


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## Dpeckplb (Sep 20, 2013)

Redwood said:


> That is by design...
> Those springs are designed to allow the valve to open at the rated pressure of the valve, and they actually are quite precise...


I agree with you. That said there was a bunch we've had that were rated at 75 psi put were blowing off at 45-50 psi. This was when we were told about the weak springs.


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## tims007 (Aug 31, 2013)

MTDUNN said:


> This saddens the owner of the vineyard greatly because there be no fine Pinot Noir this year.


DAMN IT i was hoping for some good wine this year too


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## gear junkie (Jun 20, 2008)

Not a leaking issue but the opposite. We have hard water here and it causes tp valves to become inoperable because of mineral buildup.


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## 422 plumber (Jul 31, 2008)

gear junkie said:


> Not a leaking issue but the opposite. We have hard water here and it causes tp valves to become inoperable because of mineral buildup.


Same here

Sent from my iPhone using PlumbingZone


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## timrath (Sep 28, 2013)

Same here in New jersey really really hard water


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## UALocal1Plumber (May 13, 2009)

I have often been perplexed at the common approach to T&P valves. Generally a tech will state that he "tested" the valve by operating the manual lever and witnessing water flow. But all he was doing was verifying that it opened. He has no way of knowing at what pressure the valve will open if there is an overpressure condition. 

It's absurd to try to test the valve with an air compressor or hydro test - if you're pulling the valve off for that, you may as well replace it. 

Also in my opinion, if we're answering a call for a leaking safety valve, I would like to condemn the safety valve because it has a) been used and therefore can not be relied upon to work properly in the future and b) the words "safety valve" are good at selling things and a client will generally feel comfortable replacing such a device if it lends itself to better health and safety.

As far as why they leak... The list above is good. Generally it's going to be a waterlogged expansion tank or an RPZ installed with no expansion tank.

Keith


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## Redwood (Sep 8, 2008)

A good read on why T&P Valves Leak Click Here...


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## philoplumb (Nov 25, 2013)

Redwood said:


> A good read on why T&P Valves Leak Click Here...


Thanks, I've got a commercial 480v that's blowing. I diagnosed as thermal expansion tank failure as it is full of water. I have not checked the element/thermostat reset yet as it is on a shelf 8+ feet off the floor. I will definitely check this before I proceed. The expansion tank and T&P will still need to be replaced. I just want to make sure THEY were the real problem, not a result of a greater problem. Thanks again. I am grateful to have the PZ.


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## younger-plumber (Sep 12, 2008)

I was taught that the t&p valve was a one time use safety mechanism and that once it begins to leak or blows off should be replaced.


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