One heating zone just won't cycle on, the other zone is fine

Old 12-19-13, 11:45 PM
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One heating zone just won't cycle on, the other zone is fine

Hello Everyone,

New user "Marktro" has a similar problem I am having in a different post however, I have a gas furnace not a boiler and the second-floor zone the issue. Here is my problem...

My home has 2 zones; first floor is one zone and the second floor is the second. Both zones are controlled by separate Honeywell thermostats. The furnace seems to work fine for the first floor zone. It cycles properly based on the program temps on the first floor t-stat (either by program or manual override). The problem I am having is that on the second floor, the furnace is not cycling on consistantly. You can see "heat on" on the screen, yet the furnace only turns on about 50% of the time. When the thermostat calls for heat, I hear the turning hum of the Belimo LMB24-3-T actuator, I see it turn but instead of hearing the whirl of the fire athen fan, it's followed by silence . I know the furnace is working because it will come on and turn off as it should for the first floor which as I said above is controlled by a separate thermostat. This started happening a couple of weeks ago during the abnormally cold temps of -10 to -20F. I looked into Honeywell's online manuals and troubleshooting information however, there doesn't appear to be a battery to change and the thermostat seems to be fine. Out of despiration, I flipped off the system at the breaker, waited a minute, then flipped it back on. No change.

I read that "Marktro" replaced the valve power head and had luck however, I have a different system and don't know what my heating problem for my forced-air furnace could be. Can anyone offer some advice? Any help is appreciated, David.
Old 12-20-13, 01:50 AM
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Your forced air system is a completely different animal than the hot water system in the other thread. Without knowing many more details it is impossible to even venture a guess as to what may be wrong with your system.

I will say this, it is possible that you do not have a true two-zone house but instead have a temperature limiting system. In this system there are dampers installed in the ducts leading to specific rooms that operate under control of a thermostat in the specific room. This secondary system has NO control function tied back to the furnace and acts to keep a room cooler in the heating season by closing the damper to additional heat when the furnace is in operation AND when the temperature in the room is at or above that thermostat's setting. A similar action can also work in the cooling season to limit the cooling in that room.

Or, you might have a full-meal-deal two zone system where each thermostat retains full control of the system and either thermostat can fire the burner along with motorized dampers directing where the heat (and cooling) is directed. These systems are quite a bit more complicated than the simple limiter system I first described.

Post the manufacturer and model of every bit of equipment associated with your heating/cooling system and also a few dozen (yes, dozen) clear, in focus and well-lit pictures of all these components. Add in several general photos from a far enough distance that we can see how the parts fit together. Lots of talented amateurs and skilled professionals here to help you.
Old 12-21-13, 01:07 PM
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Excellent reply from Furd. If this is a true 2 zone system, when the damper opens, there is often an end switch which closes a circuit to turn on the furnace. Often these switches are on the damper motor but can even be inside the duct. How many wires go to or near the damper motor? If three or four, there is likely an end switch involved.

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