In a forced hot water heating system, how much heat should leak from one zone to
another? I live in a two story house in New England. When built, it had one zone
for each floor. There is a fireplace in the family room, and doors make it convenient
to isolate the family room and kitchen from the rest of the first floor. Since we
have a fire in the fireplace most evenings during the winter we had long considered
making the first floor two zones, for a total of three zones. A recent kitchen
remodeling project required some other plumbing changes, so we decided to add the
extra zone. When the entire remodeling project was done, we noticed the radiators
were hot in the first floor rooms of the no-fireplace zone, even when the thermostat
for that zone was turned off. Investigation revealed that the electrical contractor
had wired all the thermostats together; when any one called for heat, it caused all
three to call for heat. This problem was fixed, but the experience made me check the
system frequently for other problems. I found the no-fireplace zone radiators were
occasionally warm, even with the thermostat off. This happens most often early in
the morning. All zones are turned down overnight.

I don't know if this is normal or a result of the installation of the extra zone.
I don't recall ever feeling the radiators before.

Here is the configuration, in case it helps. The house is about 35 years old.
About 25 years ago I replaced the builder special by a Peerless boiler and
Beckett burner. Closest to the boiler is the pump for the no-fireplace zone.
It was installed with the replacement boiler & burner. Next is the pump for the
second floor zone. It is the original, huge, Red baron. Next is the new pump for
the kitchen and family room with the fireplace. All are properly on the return
side and the flow arrows all point down. All the thermostats are on the correct
side of the doors that divide the first floor into two zones, and now they are
connected to only the correct pump relay.

I can provide more detailed information if that would help.

Is this normal? If not, is it worth fixing? How?

Thanks much.