comcastss news groups wrote:
While cleaning my crawlspace Sunday I notice water squirting out of my
furnace.
We are on a service plan so a technician was out to the house within a
couple of hours.
He replace a screw on valve that was on top of an "EXTROL" expansion tank.
He said the purpose of this valve was to let the air out of the system.
That's about all I could get out of him... Mr. personality!

I understand the frustration, and as the service tech does have
contact with the public, it would be nice if his people skills were a
little sharper. However, he is not an instructor. His job is to fix
what's wrong. Being peppered by questions (you may have only asked a
few, but a few questions many times a day sucks up serious time) slows
him down.

What I was trying to find out from him was what the two thumbscrews on the
top of this valve were for. one was black and one was red. Hot water had
been squirting out of the red thumbscrew.
When I tightened this thumbscrew the water stopped. I loosened it back up so
water dribbled out of it as I didn't know it closing it would cause pressure
to build up?

You were right to put it back the way you found it. If you don't know
exactly what something does, it's nuts to attempt to adjust it. You
could easily cause a far bigger problem.

While I may never touch these again I would like to know the function of
these two thumbscrews?
should they be open or closed?

The Extrol tanks are pressurized and not meant to be fiddled with.
The manufacturer suggests a yearly inspection to make sure the preset
charge and tank operation are working properly.

http://www.amtrol.com/extrol.htm

R