Water heater relief valve discharge

I'm new to the group so I apologize if there is a FAQ for this somewhere. For the last week or so, I've noticed a daily discharge of water from the temperature & pressure relief valve on my gas water heater (50 gal. RUUD Powervent). It's enough water to fully soak a bath towel. The way my discharge line is setup the water flows across a portion of the vinyl floor to the drain. It leaves a nice sized puddle without laying down a towel.
Any ideas besides a bad T&P valve? What would be a ballpark estimate for repair? (The water heater was warranty replacement in '00).
Thanks for the feedback, Mark
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Mark Sardonia wrote:

Since it's intermittent, probably not a bad T & P valve. Most common cause is thermal expansion causing a jump in pressure. This can be caused by very high city water pressure or by some device in the service line which acts as a check valve.
To find out for sure what's going on, you need to put a pressure gauge on the system. Watch what it does when the heater fires and no water is being used.
You may need an expansion tank or a combination of a pressure reducing valve *and* an expansion tank.
More info here: http://www.flexconind.com/html/wh-series_.html
Or do a GOOGLE Groups search here for "expansion tank"
Jim
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Speedy Jim wrote:

That site makes expansion tanks so what would you suppose they would suggest.
I don't know of a single house here that uses expansion tanks, guess we don't have an active dealer in expansion tanks. On the other hand, our T&P valves don't seem to leak either (unless they go bad which is seldom) although our normal pressure is around 80 psi.
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George E. Cawthon wrote:

For the problem to develop, there must be some device in the service line, such as a backflow preventer or reducing valve which can create a "closed" system. For whatever reason your neighborhood doesn't have them (I assume) so doesn't have this problem.
However, in millions of homes the problem *does* exist and needs to be addressed. Count yourself lucky...
Jim
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Mark Sardonia wrote:

If the water discharge is a new development and no one had messed with the valve prior to this new developement, then the valve is bad and needs to be replaced. If you call a plumber that is what he will do at a cost of about $65 to $70 in my area. Ontheotherhand, the valve cost about $15 and if you can get to it easily you can replace it in about 15 minutes using a pipe wrench.
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