Water heater - time to replace??

I have a Rheem 41V40, 50 gallon, gas hot water heater in our house - not sure how long it has been here - the serial number is 0502 103535. I got in the habit of turning the water off at the street when I leave for a trip any longer than a few days - it's older house, and I felt that this would minimize any water damage from a busted clothes washer line or broken water heater.
I came home this evening after being gone for 5 days, turned the water back on at the street, and the pressure relief valve for the hot water heater tripped - it's got a pipe that vents the water to the outside of the house. It stayed tripped for a few minutes (I was outside), until I got back inside and I reset the tripped valve, and things seemed fine. I could hear the tank heating, and I assumed that was because of the cold water that came into the tank when it was venting.
There's a 25x25 inch catch pan under the water heater - I guess to catch any water that leaks from the hot water heater and drain the leak to the outside through a drain pipe running out of the back of the drain pan, which ties into the pipe that the pressure relief valve uses to exit its water to the outside - between where the drain pipe comes out of the catch pan and it connects in to the pipe that services the pressure relief valve, there appears to be some kind of valve or device in that section of pipe - it looks like maybe it's supposed to prevent the pressure relief outflow water from flowing back through the drain pipe into the drain pan, instead of going outside where it's supposed to go - I'd never seen anything like that before and I couldn't see it clearly.
Now I notice that the drain pan under the water heater has a small amount of water in it - maybe a half of a small glass. The tank has refilled and reheated - there's no water on the outside of the tank, no water dripping, and no water near the pressure relief valve at the top of the tank.
Did this small amount of water in the drain pan most likely come back through that valve in the drain pipe? Or is it most likely something else and what's the fix?
Thanks very much for your guidance.
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On Nov 9, 9:30pm, "AngryOldWhiteGuy"

Years in service may be the deciding factor for replacing the water heater. Customer service at the manufacturer should be able to give the year it was made. If the heater has racked up a decade or more, it is prudent to go shopping for a new one. With a new heater, it should be safe to simply turn down the thermostat when you are absent for several days.
Joe
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in message

What you describe could have been caused by the water being turned on and off. I own a cabin, and the propane hot water heater there was installed in 1986. Last year, when I drained it for the season, I pulled the pressure relief valve, thinking it would let more air in to drain it faster and flush more scale out of it. When I refilled it, water came out the valve until I fiddled with it, and got it seated.
I would watch it carefully. Be sure that your catch pan drain pipe is operational because if it fails, it always fails at 3 AM or when you are not at home. A lot of water can flow before you are aware of it. There is a device that will shut off your water if it flows a lot, or is it when you set the device to alarm, I'm not sure, but there is something you can buy to protect your house from a catastrophic flood in case of failure. Still, it takes a bit to kick in, and in that time, hopefully the drain will take the catch pan's water out.
I'd say change it out, but at today's prices, and new codes, it can be a spendy proposition, particularly if the water just came from fiddling with the valve, and not a leak. Watch it carefully for leaks. Clean up ALL the water in the catch pan and check it daily for a while.
Steve
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On Tue, 9 Nov 2010 21:46:44 -0800, "Steve B"

WATTS makes suck a device. *
My furnace is in the attic with a drain pan, etc. It has a similar device for water detection.
_FloodSafe Water Detector Shutoff_
The site has a video or search youtube.
Features Shuts off both the water and power supply to the water heater upon detection of a leak or malfunction Testable and resettable device Full flow valve, complies with plumbing codes Visual and audible alarms alert owners to leak condition Contacts for connection to monitored alarm systems No special piping required Models for gas, electric and oil fired water heaters Available for and 1 in. piping
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Well squat. Her is the link.
http://www.watts.com/pages/whatsnew/floodsafe_wds.asp
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AngryOldWhiteGuy wrote:

A couple of problems here, One- Anytime an old P&T (pressure and tempurature) relief valve opens it is apt to leak, you are supposed to test them every 6 months by flipping the lever on them, but almost no one bothers to do that and when they do it is apt to leak because it doesn't seal again. Two- when you shut the water off you make a closed system and when the tank comes on it will increase the pressure on the closed system, so when you shut the water off, open a faucet somewhere so the pressure won't build up and cause the P&T relief valve to open.
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Exactly what happened at my cabin. I won't be touching that valve ever again. Opening up the lines and faucets lets enough air in there.
Steve
Heart surgery pending? Read up and prepare. Learn how to care for a friend. http://cabgbypasssurgery.com
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On Wed, 10 Nov 2010 07:53:47 -0800, "Steve B"

I'll not even drain / flush a WH, much less tamper with the TP valve.
Lived most of my life and never flushed one or messed with the valve.
Fist time I did this, the WH failed/leaked in a month or so.
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On 11/9/2010 9:30 PM, AngryOldWhiteGuy wrote:

It's not unusual for a small amount of water to wind up under a gas water heater that's been fired up for the first time or after an extended down time. The "small" amount of water is due to condensation from the flue going up through the center of the heater. You won't see the water again after everything gets up to normal temperatures. The standing pilot will prevent the formation of condensate until the heater is shut down again. The colder it is, the more likely it is for condensate to form. It also depends on the run time of the burner and incoming water temperature. High efficiency furnaces that extract all the heat from the combustion of gas have a drain to get rid of the condensate that forms. I curious about the location of your water heater and how cold it was when you fired it up?
TDD
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The water heater is inside the house and it wasn't really cold at all here while we were gone - in the 60s.
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On Nov 10, 7:24am, "AngryOldWhiteGuy"

Agree with the points others have raised, in particular that the TPR likely opened because with the main shut off, when the water heated, there was no place for it to expand and the pressure got too high. Given that it failed to close properly, I would at least replace the TPR valve. You can get one at HD or hardware store. I'd consider the age of the heater and the consequences of it suddenly leaking and consider replacing it. Typical life for a gas one is probably 13 years. A lot depends on your water, so experiences of neighbors could be helpful. Usually when they fail, it's a reasonable size leak, not a sudden catastrophic burst. But the consequences of such a failure and your tolerance for risk vary.
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On 11/10/2010 6:24 AM, AngryOldWhiteGuy wrote:

When you light one up that has been off for a while, you can watch through the access panel where you light the pilot and see the drip of condensate coming from the flue. Of course the water in the pan could have come from the TP valve too.
TDD
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I don't know about the condensation - but all I did was turn the water off at the street - with the tank still full of water, the gas would still go on and off to keep the water at the temp set by the thermostat, right? Meaning that the water would still stay hot, just like it does when we're home??
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On Nov 10, 2:54pm, "AngryOldWhiteGuy"

Yes, but as the water and air in the water heater heated and expanded, there was no place for it to go except out the pressure relief valve. Water and air do expand when heated, not a lot, but enough to do what happened to you.
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On Nov 10, 3:54pm, "AngryOldWhiteGuy"

Yes and I agree, the condensation is a non-issue because the tank was always hot and whatever water you saw didn't come from that.
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On Nov 10, 3:54pm, "AngryOldWhiteGuy"

many areas now require a backflow prevter at the meter, and a pressure tank to prevent the T&P valve from opening.
its like your main valve is shut off
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