Leaking Water Heater Valve

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That's a pressure relief valve, it blows off on high temperature or pressure. Either a control in the unit is allowing the temperature or water pressure to rise beyond what it should, and the valve is just doing what it's there for, or the valve has gone bad. The valve screws on to the fitting and appears to have some type of dope or sealant on it. There is also a possibility that the building water pressure is to high feeding into the heater
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

My best guess was that it might be an over-temp/pressure valve. Similar to a thermostat in a car. I think it might be in need of replacement. I lowered the temp on the heater, and it seems to be OK. Except, that the water temp is now a bit too low for my liking. I also figured it was threaded and 'doped' from it's appearance. Might just head off to the plumbing supply joint in the a.m., a get a replacement. I doubt it's a pressure problem. The house is on it's own well, with a fairly elaborate filtration system. I ain't afraid of no pipes.
-- Steve M
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
mcsteve wrote:

Sure it's an overpressure valve, they need regular maintenance dependant on the quality of the water supply. They just "cake up" with calcium or salts in general, they are spring loaded and so need to be properly set up with a pressure test. INMHO if you count the number of turns to remove the spring loaded plunger valve and re-install with the same number of turns after cleaning up it should be within a practical distance of the original setting. Of course the correct way is to use a pressure tester and calibrate it to your local code setting. The instructions for these usually say to operate the lever once a month or whatever to clean it but in my experience it becomes necessary to "huck" 'em out when you see the build up of salt around the outlet and pipe connection.
Cheers .......... Rheilly P
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
It's a pressure relief safety valve.
Turn the water off. Drain the tank. Take off the old valve using two wrenches (probably pipe wrenches, but channel locks or crescent wrenches may work if that's what you have) -- one to hold the copper pipe fitting so it doesn't twist, and one to turn the valve to unscrew it out. Take it to a hardware store and buy a replacement. Get either pipe dope or Teflon tape for sealing the threads on the new one you put in.
Ordinarily, the valve should have an open pipe that comes out of the bottom of the valve and that goes down to about 6" to 12" above the floor. That's so no one gets scalded with hot water if the pressure relief valve opens up due to high pressure -- the water gets directed to the floor (or to a pan or open drain) instead. There needs to be an air gap at the end of this open pipe -- meaning it cannot be connected directly to a drain line, etc. -- so there cannot be any back-flow of water from the drain into the tank.
The hardware store will have the fitting and pipe that goes from the relief valve to close to the floor or drain. They're cheap and you can use PVC so you don't have to solder anything.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Here are two YouTube videos on the subject:

http://www.youtube.com/watch?v=5Sm5dHAqTcI


http://www.youtube.com/watch?v=pVxPt6rwHn8


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.