David wrote:
snipped

David,

Does your system use circulator pumps? Probably yes, unless it's really
ancient.

If it does, Then I assume that you've already determined that those
pumps are *not* running when you're finding the pipes and registers are
warm when they shouldn't be.

You may have a "gravity valve", properly called a "hydronic flow check
valve", which is intermittantly sticking open and allowing water to flow
through the piping even when the pump isn't running.

Those can be simple weighted valves which are easily pushed open by the
water pressure created by a circulator pump, but will prevent water
flowing through thermo-syphoning action. (Hot water is lighter than an
equivalent volume of cold water, you can work out the rest. The Model-T
Ford circulated its cooling water through the block and radiator that
way - without a water pump.)

These valves come in a variety of shapes and pipe sizes. Here's a link
showing what one type looks like:

http://www.conbraco.com/products/ph/...on=D&pid=35-FC

If you can't locate valves of this type in your heating system, they
just may be integral to the circulator pumps. Some have been made that way.

If you find that valve you could try a brute force approach and give it
a couple of taps on the side of the head with a hammer to see if you can
jar it closed so the affected pipes will get cold. That won't provide a
permanant fix, they'll still have to be taken apart for cleaning, or
replaced.

Depending on your technical prowess, available tools, and courage, you
may well find it best to leave the job to a professional. The tuition
cost for a DIY heating repair education can escalate pretty fast if
things start going wrong. G

Lastly, I have to agree that your posting your question to a
"professional group" wasn't worth wasting address keystrokes on. Those
guys are still stuck in a medieval guild mentality and for reasons I
can't fathom or appreciate, they seem take immense pleasure out of
acting like a bunch of 14 year olds in the school cafeteria, bullying
folks who aren'r in their little clique. Leave 'em to themselves, they
deserve each other.

Good luck, and let me know what the problem turns out to be.

Jeff

--

Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can smile when things are going wrong, you've thought of someone
to blame it on."