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

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

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.