Heat upstairs, but not downstairs + other strange observations

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Old 01-15-13, 11:16 PM
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Heat upstairs, but not downstairs + other strange observations

Hello,

I have a two-zone system (upstairs and downstairs) using a Bryant gas furnace (310AAV or similar - not sure, lost the manual and the furnace is in the attic... so it is not easy to get to) controlled by two Honeywell TH44110B thermostats. The system is about 6 years old and lightly used.

On the thermostats, I have a white wire going to W, a yellow wire going to Y, a green wire going to G, and a red wire going to a shorted Rc and R.

Of the two zones, only the upstairs works when I turn it on for heat. I can hear the furnace start up and after about a minute the blower kicks in and I can feel heat through the upstairs vents. All checks out.

It's a different story downstairs. When I turn on the thermostat for heat, nothing happens. I don't hear the furnace in the attic and the blower doesn't come on. I tried swapping in the upstairs thermostat (the "good" one) and no luck either.

A few other observations:
  1. If I plug in the downstairs thermostat upstairs, upstairs doesn't work.
  2. I can manually turn on the fan downstairs by switching the Fan to "On" from "Auto". It only blows cold air though so that's not what I want. But it baffles me that this works manually.

I have limited experience with furnaces, thermostats, and hvac technology and would very much appreciate any clues. I do have a multimeter and sort of know how to use that.

Thanks!
Ryan

 
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Old 01-16-13, 08:23 PM
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Since the fan comes on when you switch the fan to "on" at the stat, we know the stat is getting power.
I can find nothing on Honeywell's site about a Th44110B thermostat. That number doesn't look right. Please verify. Honeywell thermostat numbers are usually a TH followed by 4 (not 5) numbers, a letter, and 4 more numbers.

Is there some sort of zone control panel? For some reason, you are not getting 24V back to the furnace on the white wire.
 
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Old 01-16-13, 10:47 PM
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Those TH4110 stats are junk. I have measured high resistance across the closed points behind the stat.
You want a 6000 series or higher Honeywell stat.

When you move the broken downstairs stat upstairs it doesn't work up there either. This proves that you need a new stat.

I recommend replacing the other TH4110 as well.
 
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Old 01-17-13, 10:55 PM
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Oops, Houston204 is right: the thermostat is a TH4110B. Can I just go out and buy a new thermostat and plug it in where the Honeywells are?

Yes, there is a zone control panel, it is up in the attic on top of the furnace. How can I check if 24V is going back to the furnace?

Thanks for all your help!
 
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Old 01-18-13, 03:46 PM
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I know you don't want to hear what I think of zoned systems. I'm going to bow out of this thread.
 
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Old 02-04-13, 01:43 PM
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Thanks for the help so far. I would like to add some new information from my poking around in the attic this weekend.

I found out that the damper actuator for the downstairs vents is broken; the gears are stripped and thus doesn't open or close. The model number of the actuator is Honeywell M847D1004. The other actuator for the upstairs vents seems to be okay, but I imagine that it will only be a matter of time until it needs replacing.

Is the fact that the actuator is broken a related issue to my overall heating problem? Is replacing the actuator a fairly simple job, and would I be able to accomplish it on my own?

Thanks. I'm excited that I've found another issue... feels like I'm getting somewhere.
 
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