Gas Hot Water Heater Discharge from T&P Valve

[elebert]

My gas hot water heater releases about water at a rate of about a half a galon a day (not continuously).

Last night, my wife was going to take a shower and the water was luke warm, so I went down to the basement and turned up the heat from "pretty low" to "medium-high". Hot water came, everything good. This morning, our basement had 10-15 galons of water in it released from the T&P valve. Also, the valve was releasing water while the gas burners were on. I shut the gas off, and the heater's cold water supply off. It continued to releave water for about 45 minutes. The water being released wasn't very hot at all, but it was warmer than "luke warm".

There, I've given all details I can give. Any advice?

[LazyPup]

Sounds like you have at least one and possibly two relatively minor problems.

Question, are you experiencing any water hammer (a loud banging noise in the pipes when a faucett is turned off?) If you are getting the banging sound your problem is in the water hammer arrestors as you will see when you read on.

Technically speaking, water reaches maximum density at about 39 deg.F. If water is then either heated or cooled from that temperature it expands. During winter months the ground is colder, hence the supply water is colder, often very near the 39 deg maximum densitity temp. As the water is heated it then expands which increases the volume and pressure in the water heater and piping system. Normally the water hammer arrestors have sufficient capacity to absorb the increase in volume.

The water hammer arrestors are simply a short stub of pipe in the order of 12" to 18" installed veritcally with a cap on the top. They are usually installed inside the walls at any convient point near the top of the water distribution system. When first installed the entire piping system is empty and as the water is turned on, filling the lines air ir trapped in those risers. Air is compressible, whereas water is not, so the air trapped in the top of the water hammer arrestors can compress to absorb changes in pressure or volume.

In areas where the water supply pressure exceeds 85psi we are required to install a pressure regulating valve on the supply at the main, and an expansion tank above the water heater.

Although it takes a considerable amount of time, air can be absorbed into water, which results in the water hammer arrestors loosing their charge of air and negating their function. The simple solution is to turn the water off at the main, then drain the water distribution system down by opening a faucett at the lowest point in the system, usually a laundry sink in the basement, or an outside hose faucett if there is no basement. During the draining phase it is best to open both a hot and cold faucett near the top of the distribution system (if a two story open the faucetts on the upstairs bathroom sink.) Opening the faucett provides a vent to allow air into the system which will aid in draining it down. Once the system has drained down, close the faucetts and open the main. The system will once again fill with water. During the filling process a new charge of air is trapped in the water hammer arrestors restoring them to full operation.

You will then have to go to each faucett in the house and open the faucett to vent off the excess air. Expect a lot of sputtering as the air vents, but once you have restored full water flow, move on to the next faucett until you have full water flow at all points.

The water hammer arrestors should now have a sufficient volume of air to absorb water expansion as it is heated in the water heater.

If recharging the water hammer arrestors does not solve the problem, the next step is to replace the T&P valve.

To replace the T&P valve you have to first disconnect the T&P valve overflow pipe. (if it is rigidly soldered you may need a tubing cutter to cut the tube before unscrewing it from the T&P valve.)

Turn the water heater burner off, or in the case of electric heaters, turn the breaker off.

Close the shutoff valve on the water heater cold water supply line.

Open the bottom drain cock to drain the tank slightly. You need not empty the tank but the level should be below the T&P valve location.

Have your new T&P valve ready to set in place, with pipe dope on the threads.

Use a pipe wrench to unscrew the existing T&P valve and remove it. Screw the new valve into place, tighten it snubly and align it so you can re-attach the overflow line.

Open the cold water supply valve and turn the breaker on or re-light the burner.

You will then have to again open a hot water faucett to vent off the excess air that got into the tank while changing the valve.



You can get T&P valves at any hardware or home supply plumbing department for about $12 to $15.

[elebert]

No Banging. Also, there is no expansion tank and I'm pretty sure there's not regulator valve on the intake. Just an on/off valve.

Does this mean my T&P valve is relasing prematurely? Also, are all T&P vavles the same?

[LazyPup]

With some rare exceptions the T&P valves are the same. The plumbing code states they must regulate pressure below 150psi and temperature below 210 degF.

The only major consideration is the discharge diameter of the valve. In most residential applications the discharge diameter will be 3/4" and the discharge line must be equal to or greater than the discharge diameter of the valve. Absolutely do not be tempted to save money by reducing a T&P discharge line. Reducing a 3/4 line to 1/2" cuts its volume in 1/2 and thereby negates its ability to protect your home.

line capacity is determined by cross sectional area rather than diameter , therefore to compare line capacity you must use the formula Large diamter squared divided by small diameter squared.

thus 3/4" compares to 1/2" as,,,,

3/4 x 3/4) / (1/2 x 1/2) =
(.75 x . 75) / ( .5 x .5)=
0.5625 / .25 = 2.25

which means a 3/4" line has the same capacity as 2.25 lines of 1/2"

[elebert]

Well, I drained my house and refilled it, picked up a T&P valve and installed it, and not a DROP so far. I could easily feel the difference between my old valve and the new valve.

That's two appliances you've saved me thus far LazyPup.

Thanks,
Ed Lebert

[LazyPup]

sounds great,,,we get one more an i'll have to put you on the payroll...