Mike wrote:

Jim,
I also have a problem with my ho****er system. I went down to my basement
and water was spewing out of the bottom of my pressure reducing valve. I
notice that there seems to be a plug which is missing. Are these parts
readily available or do I need to replace the whole unit.I am not sure of
the model of the valve. Looks like 2 valves in tandem right after the water
inlet.



That's a dual control. First, a pressure reducing valve
which is set to maintain a specific "height" of water
in the system.

Second is a pressure relief valve which opens when system
pressure exceeds (usually) 30 psi.

The relief valve has a discharge port and that may be where
water is escaping (as it should).

Typical style:
http://www.cashacme.com/genheating.html

See what the boiler pressure gauge reads. Normal is 12-15psi
(depending on building height, of course). If way over that,
the valve may be relieving for good reason. If normal range,
the relief valve may be defective.

Jim