Yup, that's a tempering valve!

The plastic part is supposed to turn, but if it hasn't been moved in years, attempting to turn it would probably make the
leak worse.

Unless access or shutting the water off is a problem, should be an easy replacement job for a plumber.

Eric Law

"grodenhiATgmailDOTcom" wrote in message oups.com...
I have a 5 year old boiler (which also provides hot water service for
my house), which seems to have a leaky what I think is called a
tempering valve (see link below for pic).

http://www.pexsupply.com/img/categor...0A%20Valve.jpg

This valve is right outside the boiler where our hot water service
comes out (ie not the baseboard runs). There is almost a constant 2
foot x 2 foot puddle right under the valve (especially after hot water
use, like showers, laundy, etc). I've watched it closely and this
valve is definately the cause. It look like water is making its way
up the stem (against gravity), and leaking from the underside of the
valve handle (that black plastic part in the picture). It's been
doing this for about 6 months but recently has been slowly getting
worse. I've tried turning the plastic part but it seems to not want
to budge (I don't push too hard b/c I don't want to break it). I was
hoping turning it a bit may reseal the leak. I guess first
question... Is it supposed to turn? Next question, how big a job is
it for a plumber?? I'm guessing just switching out the valve should
be a quick one?? And finally, how common is this?