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Old 10-02-2011, 04:13 PM   #1
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Thermostat/Furnace weirdness


I have an old Clare megasave, and it has been giving me some strange issues lately. It was serviced just last spring, and the tech ended up replacing the sequencer, igniter, and ignition control module (which was the actual problem)

Firstly, a problem that has been happening with the new Honeywell UtilityPRO thermostat is that after switching it to heat yesterday, it will go blank every 10 minutes. From looking around the net, I found the cause is likely to be the temperature limit switch tripping and cutting 24V power to that stat. Makes sense, as my furnace has been running VERY hot in the last year or so. SO hot that the ducts are untouchable. The tech told me that was normal, and I'm certain it is not, as it has never run that hot. The other thing is that when I called in about the limit switch tripping, they said it was normal and that it was the peaksaver thermostat's problem, and that I should call my power utility company to get it looked at. Not convinced.

Another issue is that both this utilitypro, and my previous Honeywell FocusPROTH6000 series appear to kill the heat too early. By too early I mean the fan doesn't get a chance to start yet, and the thermostat just aborts the heat on signal and the furnace ends up sitting. Even more strange is the fact that the fan will sometimes turn on a few minutes after the furnace stops. Thermostat idle and the fan will turn on by itself a few minutes following the aborted heatup.

Any advice about what I can do/what I can tell the service tech to check? I'm under a service plan, but the techs seem to be more willing to just do the bare minimum, say everything is fine, and then try to sell me on a new furnace

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Old 10-02-2011, 05:35 PM   #2
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Thermostat/Furnace weirdness


the only thing the stat does is call the heat in thru R to W on the stat.within the furnace there are two limits one is the HI-LIMIT if the fan stops or filter gets blockked up and it will knock the gas burner down till it cools off then the burner will restart...fatigues heat ex....limit 200F-220F trip ranges this is a safty trip should stay closed with clean filters and fan squirrel cage..check that.no for the FAN=LIMIT when the stat calls the burner heats up the heat-X and the fan limit closes to supply the air as long as the heating burner is running the fan should run.....so now the stat satisfies gas cycles off but the fan will stay on til it cools the heat-X off 60F range and stops the fan.the reason you hear the fan run during a short burn the fan limit picks up the heat and closes the fan limit and the fan runs...till it cools....that duct being too hot is something needs to be checked tell this brain surgeon to put a thermometer in the supply duct to see what temps the limits cycle.if you remove the stat off the subbase you will see that R to W that is your heat closure point on the stat...its low voltage jump it out to see if you get a better run cycle on the furnace stat might be causing the problem..check those squirrel cage and have him verify the fan limit temp range stamped on it vs the hi limit also stamped... example 200F-220F opens fan limit 50Fopens-175Fcloses

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