Black Splat

I have a gas hot water heater in my basement. It looks as though black water shot out of the pressure relief tube. There is a large splat mark on the floor of dried black residue. The splat is about 6 feet in diameter.
I tested the relief valve...clear water came out.
Otherwise, my hot water has been fine and the water clear.
The only factor i can think of is that i left the house vacant for a week. During that time i shut off the cold water supply from the street.
Does anyone have any thoughts on this?
Thanks Aabob
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Bob wrote:

Shutting off the water supply may have caused the problem by creating a closed system so that when the water heater came on the expanding water had no place to go other than out the overpressure relief valve.
That's if you don't have an expansion tank in the system of course.
Jeff
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Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
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You're on to something.
On a very slightly related moment, a friend of mine had the power off, at a house he was trying to sell. Winter, cold. I suggested to drain the pipes, which we did. Find out later, he'd closed the toilet valve, and the water split the (copper) tube from the shut off to the tank valve.
I went and bought a nylon braided tube, and put the plumbing back in action.

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wrote:

Jeff is right on!!!!!
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Why would you heat hot water? (Someone had to say it.....)

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wrote:

Because it tends to cool, if not heated?

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On 12/3/2011 1:35 PM, Bob wrote:

If I remember correctly, hydrogen gas can build up in a water heater. The metal of the anode rod reacts with the water producing the gas.
http://www.wh2only.com/homeowners/basics
http://preview.tinyurl.com/88zwpyk
https://www.ridgidforum.com/forum/t15767 /
TDD
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On Sat, 03 Dec 2011 22:02:44 -0600, The Daring Dufas

Hydrogen sulphide too, if there is sulphur in the water.

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