Question on furnace/thermostat

[the_bird]

OK, quick question for the experts in the room.

Went to turn the heat on in the house, and nothing happened upstairs. We have two thermostats, one upstairs, one downstairs. Turn the heat on downstairs, furnace turns on fine. Hot water is fine. Turn the heat on upstairs, bupkis.

Sound like an issue with the thermostat upstairs? It's OLD, like, you take the cover off, and there's a glass bulb filled with mercury. VERY cool, actually

Sound like I just need to replace the thermostat? Anything else it could be? DIY project? My old man is handy as hell (old-school Vermonter), he'll be down tomorrow anyway to help me sheetrock; something we'd be able to do ourselves?

Thanks, bros!

 

[user 574]

Sounds like just a thermostat but does it run a separate furnace? I'm trying to understand the two thermostat setup... Electric heat?

 

[the_bird]

Oil. One furnace that heats everything, two heating zones plus the hot water.

 

[LouT]

Woah, bird. Before you rip the antique thermostat off the wall, hang on.
I would guess that you have forced hot water heat. If so, there's circulating pump(s) and solenoid actuated valves that control water flow to each zone. When one of my zones wouldn't come on last year, I peeked around and found a wire to one of the solenoid valves had broken right near where it was stripped bare and screw-connected. You know, how wire does if you bend it back & forth too many times.
Those old thermostats almost never "fail", unless you hit it w/something it's probably fine. Look elsewhere first.
BTW, the programmable thermostats are great, not very expensive, and can help you save money.

If you have forced hot-air, your multiple zones are possibly controlled by an electromechanical damper that would have a small motor on it - look there for trouble.

Any other stuff comes up, ask -- I don't work in the field but I'm pretty handy.

 

[LouT]

Oh, one other question- - if the zone that works is NOT calling for heat, and the zone that isn't working IS calling for heat, does the furnace ever actually kick on?

 

[the_bird]

No. Whether the working zone is calling for heat or not, the upstairs doesn't work.

 

[david_42]

If you turn the upstairs thermostat on, does the furnace actually light? With a dual zone system, either thermostat should start the furnace, even if the circulation pump/fan/damp doesn't operate for that zone.

The first thing I'd check is for voltage at the thermostat. Most of them are 24 volts.

 

[Bobby_M]

One way to bypass the thermostat is to just twist the wires together at that location. The one you're describing is a simple make/break switch. If it doesn't come on, then you can rule it out. Next, leave those wires twisted together and trace them back to the furnace. Remove them from whatever they are connected to and jump those terminals together. If the furnace fires, you know there's a break in the wire. Those are the two easy checks. From there it gets more difficult.

Because it's also your hot water source (my parents had this system too), the furnace will always fire to keep the water in a certain range. The thermostats basically just regulate whether or not the circulation pumps run. Therefore, jumping the thermostat wires should make the pump run right away. Systems that don't make your hot water will sometimes fire first and then run the circ pump after the temp is up.

 

[Radarbrew]

At your zone valve if the pipe is hot before and cold after the zone valve it isn't open. If your calling for heat, and the furnace don't fire, it probably isn't the thermostat. One of those mechanicals hardly ever go bad. That's why they were used for years. Your best bet is check the wires at the thermo, and at the switch box on the boiler. Be careful there's voltage there. BTW we use the same setup, 2 zones and oil heat.

 

[the_bird]

Well, thermostat is fine, second set of eyes helped me confirm that. I've got to get a furnace guy in anyway (time to clean the bugger out), so I'll let him sort through all the details. At least half the house is warm, and heat rises!