hi..my house is hot water heat, built ~1980 in northern NJ, 3 zones before we added an addition (basement), first floor, 2nd fl. We now have a 4th zone ("kitchen").

my basement has been overly hot for a long time, but I finally spent a day trying to narrow this down and have concluded that: when my first floor is heating, hot water is also sent through the basement (all 3 loops of it).

I am pretty confident this is a plumbing situation, as I even disconnected power from the basement zone, confirmed the electronic valve was closed and then manually closed the shutoff for that zone, and I confirmed the situation still to occur.

What also puzzles me is that when I try the reverse, e.g. let the basement call for heat, the first floor zone does not get hot.

The only thing I can figure is that somehow the first floor zone is plumbed to the basement such that the basement zone can return through the first floor. Nothing else would seem to explain how I can physcially close the return from the basement and still that zone would heat up, unless it has some other way to return.

Do you think this is somehow by design, or is it some type of plumbing error, which would not surprise me given what else I've seen in this house with the electric. Was this some theory that would keep the first floor warm, or what. Has anyone ever seen something like this?

Trouble is the basement is finished, and some of the returns go behind walls so I can't quite follow all of the basement loops to check this out.

Any suggestions? I feel like we are spending money to heat where we don't have to.

THANKS IN ADVANCE!!