On Sat, 03 Dec 2011 22:02:44 -0600, The Daring Dufas
wrote:

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

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

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

https://www.ridgidforum.com/forum/t15767/

TDD