Dual Thermostat - Upstairs Not Working

We have two thermostats, main floor and upstairs, for two separate zones of a hot water baseboard heating system. It's starting to get cold and I noticed that the upstairs thermostat (an old White-Rodgers 1F56-301) isn't turning on the furnace. (It does work fine with the a/c for the upstairs.) Should the second floor thermostat work independently of the first floor thermostat (which does turn on the furnace)? I don't even see where the 2nd floor thermo is wired, whereas I can trace the 1st floor one directly to the furnace.
Even though my wife would like it fine if the upstairs stayed freezing, it's getting a mite too cold for my tastes.
What can I check?
Thanks!
--
jwayne@_no_spam.com

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Possibilities: Bad thermostat Bad zone valve bad pump for the upstairs bad wiring The AC unit may power the thermostat, did you leave the power on to it?
When you say hot water, do you have 1 ir 2 pumps, zone valves? Did you bleed the air vents upstairs? Did uou check the water pressure in the boiler? Water pressire on the boiler should be 1/2 psi per foot the baseboard is above the boiler + 5 PSI. More insormation would be needed for a better answer.
Stretch
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Like Stretch said, there are many possibilities depending on the particular equipment you have. If you open the thermostat, look for terminals marked RH and W, put a jumper wire across them and see if anything happens at the boiler. If so, you've got a bad stat, but beyond that, the sequence of events depends upon your equipment, zone valves, circulators and relays

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thermostat: check for proper 24 volts at the upstairs thermostat. if the upstairs thermostat is broken you might alligator jumper its wire pair that calls for heat to test it while the downstairs thermostat is turned down.
water: if radiators are dry you won't get heat. check for missing water in the upstairs loop. [let the air out of the bleeder valves while adding water to the system.] this is normally done in summer. cold water added to a hot boiler slowly never to a dry hot boiler or damage can occur.
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