Hello all...

I have an on-demand gas fired water heater. It is an Aquastar, model
# AQ 125-B. Recently, it has been leaking through what I believe to be a drain
valve. When I run the hot water, the valve spews and won't shut off. I have to
shut down the supply line and after I wait a bit it will cease leaking.
I want to know the purpose of this valve, and why it's 'acting up' in this
manner.

Photo of valve: http://i37.tinypic.com/s41hrm.jpg

Photo of heater: http://i34.tinypic.com/30t1a43.jpg

The valve is mounted about 12" below the heater. Unit
is a wall mount. Valve is at the end of a horizontal cross
member that's 'teed' off the vertical pipe that I assume is
the outlet from the heater.

Hoping I can fix this myself. I've done my share of soldering
pipe in the past. This fitting appears to be glued, rather than soldered.
It is threaded.
I don't want to call a plumber.


TIA
--
Steve M