water heater venting water outside from what I think is mixer valve

**montags** · 09-30-2012, 03:56 PM

Hi,

I have a gas powered water heater tank that is continually leaking hot water outside via what I think is an overfill pipe. Having looked at diagrams online, I think it is coming from what is called the mixer valve (please see photos below). I originally thought it was coming from the pressure relief valve (PRV), but that is a separate plastic pipe and is not leaking. Note that I have two vent pipes to outside, one from the PRV and a second from this "mixer valve" thing.

I did test the pressure relief valve and it seems to be working fine. Flows when I open it and stops when closed. When I do operate the PRV, the venting of water from the "mixer valve" stops for a minute then starts dripping again. It is a vigorous drip, maybe a few gallons per day. We have no complaints about the volume or temperature of our hot water.

The water heater is 13 years old and despite having the manual, I do not know what manufacturer it is. There is no ID on the manual, not even a name. We live in a soft water area and this heater is the original install on 1999 house. Note that there is a continual ssshhhh sound like a faucet is running and it is coming from this valve.

I was hoping it was an issue with the PRV and maybe it is - I know little about water heaters.

Thanks for any help.

http://mcontact.bestmail.us/DSC_0475_new.jpg

http://mcontact.bestmail.us/DSC_0471_new.jpg

http://mcontact.bestmail.us/DSC_0474_new.jpg

Valve in question:
http://mcontact.bestmail.us/DSC_0478_new.jpg

**jadnashua** · 09-30-2012, 07:54 PM

The valve on the side tank is a T&P valve - the fact you can open it is no perfect indication that it's good.

A mixing valve would require both the hot and cold to connect to it (it's called a tempering valve). I'm not sure, but I think it's a pressure relief valve (again, not a PRV). It could be defective, or could be doing its thing...it would normally be set lower than when the T&P opens. If you have an expansion tank, it could be shot. The city could have raised the supply pressure (new pump, or new water tower, for example).

**montags** · 09-30-2012, 08:24 PM

Thank you Jim. Those are all good, well thought out points. I can see you are an engineer, so that makes sense. I think you are right, it is a pressure relief valve. I am in two minds about just replacing it because as you hinted, there could be other problems and it's just a symptom.

**jimbo** · 10-01-2012, 04:42 AM

I would investigate WHY someone, at some point, thought it necessary to install a seconday pressure relief valve. Check you system pressure both static ( no water running) and dynamic ( a faucet open)

**montags** · 10-01-2012, 06:59 AM

Originally Posted by jimbo

I would investigate WHY someone, at some point, thought it necessary to install a seconday pressure relief valve. Check you system pressure both static ( no water running) and dynamic ( a faucet open)

Thanks Jimbo. Good points. I'll raise this when the plumber is looking at it.

**Terry** · 10-01-2012, 09:07 AM

It looks to be an extra valve there.
Some areas required a relief line on the main piping, and none on the water heater. A dumb idea maybe, but that's what some inspectors wanted. Some were done because there was no way to drain a relief off the heater. We could position the relief high enough to get a good gravity drainage off the relief. Since the T&P is being drained outside, it would seem that the one higher up could be deleted.