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!

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?

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

TIA


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