> The funny thing is if I check the zone control on the boiler, the zone
> is not calling for heat, but the radiators are always hot.
I'd suspect the zone valve for the upstairs zone as well.
I have 21 Honeywell V8043C zone valves in my building, so I'm intimately
familiar with them. However, I do know that SOME older Erie zone valves
will fail in the OPEN position. That is, if the valve stops working,
it'll allow continuous flow of hot water into the radiators rather than
stop the flow of water through the radiators. I can't remember all of
the details now, but 10 to 15 years ago I remember one suite that had an
old Erie zone valve got so hot that I was telling the tenants to open
the windows to cool their apartment down until I could fix the problem.
Anyhow, I do remember that the sector gear on the Erie zone valve in
their apartment was stripped, and that when I replaced that gear, the
zone valve worked properly again and the temperature in their suite went
back to normal.
In my experience, if a Honeywell V8043C zone valve sticks, it will stick
in the closed position so the radiators will be cold. I can't recall
every having to unstick a Honeywell that was stuck open. But, I've
unstuck more Honeywell zone valves that were stuck in the closed postion
than I care to remember.
If it's a Honeywell zone valve manufactured after about 1980, then you
can replace the "actuator" (also called the "head") on the zone valve
without having to drain the heating system down. Erie zone valves are
the same way, with their "Pop Top" zone valves. That means that if the
problem turns out to be the zone valve, you can fix the problem by
replacing the actuator on that zone valve yourself.
Maybe take a look at the zone valve and post any markings you see on it.
That will tell us what make and model of zone valve you have. Most
zone valves operate much the same way, except Taco zone valves which I
have virtually no experience with.
And, while you're looking at the zone vavle:
1. Check that the valve's manual open lever isn't in the open position.
On this Erie Pop Top zone valve, you can see the manual open lever:
All Honeywell and Erie zone valves will have a manually open lever like
that, and that works much the same way.
If the valve ever craps out in the middle of winter, the manual open
lever allows you to open the valve manually to have continuous heat,
which is better than no heat at all. You just push the lever forward
(against spring pressure) and hold it down or up (depending on the
valve) so that it catches in a slot as the spring pulls the lever back
into it's original position. As long as spring tension holds the lever
in the slot, the valve will remain in the open position to allow water
flow through it. Check to see that your manual open lever isn't
engaged, and thereby overriding the normal operation of the zone valve.
2. Take the cover off the zone valve (on a Honeywell or Erie, it just
pulls straight off) and have a helper turn the upstairs thermostat all
the way up and all the way down while you watch the operation of the
upstairs zone valve. Watch the machinery under the zone valve motor,
and see if that machinery moves all the way in one direction when you
turn the thermostat up, and all the way back again when you turn the
thermostat down. If the zone valve doesn't respond to the thermostat,
check that the zone valve is getting the correct voltage (typically 24
VAC) when the thermostat is turned up and 0 VAC when the thermostat is
There should be markings on the valve which will tell you what voltage
it operates on, and normally that will be 24 volts AC, which isn't
enough to give you a shock. However, the valve may be equiped with an
"end switch". The job of the end switch is to close and thereby
complete a circuit just as the valve finishes opening. Often this end
switch is used to turn on a 120 VAC circulating pump for that zone.
(So, the thermostat opens the zone valve, and as the zone valve finishes
opening it's end switch turns on a zone pump.) So, be careful what you
touch because if you have an end switch in your zone valve, there could
be up to 120 volts AC being switched on and off by that end switch. If
there are only two wires going into the zone valve cover, those two
wires go to the motor, and you don't have an end switch.
3. The motor inside both an Erie and a Honeywell zone valve will look
Feel the motor inside the valve, and see if it's hot. If it is, that's
typical of a motor that's simply stuck, and all it needs is a shot of
WD40 to get it working again. These motors are tiny, and it just takes
a bit of friction to stop the motor from turning. If the motor won't
turn, the zone valve is stuck in whatever position it was when the motor
(However, the motor wouldn't be hot unless there was 24 VAC going
through the windings continuously, and that could only happen if the
thermostat upstairs was calling for heat, and your zone controller says
it isn't calling for heat.)
Besides any markings on that zone valve, could you confirm that your
heating system only has a single circulating pump for all three zones.
I'm presuming it's only the one pump because if you had separate zone
pumps, the zone control wouldn't be turning on the zone pump for the
upstairs zone if that thermostat wasn't calling for heat. And, without
any hot water flow through the upstairs radiators, it wouldn't be any
warmer up there.