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Old 02-11-2011, 08:47 AM   #1
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Replaced thermostat but it is still changing set temp on its own!


My digital themostat (maybe 15 years old) started acting strange lately. It would sometimes just go blank and other times it would set the temp. different from what we set it. For example, we go to bed set at 67 degrees but wake up to find it set for 64. I replaced it with a new programmable thermostat. The wiring was a piece of cake so I know nothing went wrong there. The furnace burners were also cycling on and off before reaching the temp. I got a code 33 on the Bryant Plus 80 furnace (Limit or Flame Roll-Out Switch Open). I had recently put a new high filtration allergen filter in the unit for the first time and I thought maybe that was obstructing the air flow too much. I changed that filter to the one I had been using for years (new one of course) without a problem and the furnace then seemed to work fine. I don't see the light flashing any more error codes this morning. Do I still need to worry about the limit switch or something to clear this up for good?


Last edited by Eagle One; 02-11-2011 at 09:41 PM.
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Old 02-11-2011, 06:37 PM   #2
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Replaced thermostat but it is still changing set temp on its own!


Some furnaces kill the power to the thermostat when the limit trips. That resets the thermostat to the factory default setting of 64 unless there are batteries installed. The less restrictive filter should solve the problem.

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Old 02-11-2011, 09:30 PM   #3
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Replaced thermostat but it is still changing set temp on its own!


My stat just went bad on a heat pump , flashing like your saying ....... if you know what wire is supposed to control stuff just jump them out to find out if it's the stat going bad . Home depot has a nice range of stats from 20 for another digi or 1oo for a wifi stat u control you can control from anywhere on a PC.
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Old 02-11-2011, 09:39 PM   #4
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Replaced thermostat but it is still changing set temp on its own!


Cool. Thanks for the info. That explains why it was at 64 degrees for the set temp. The new programmable thermostat seems to be working fine and it appears that the filter was indeed the problem. I had always been using Filtrete (Red packaging -1000 performance rating) but tried the Filtrete (Purple packaging - 1250 performance rating) about a month ago. It worked fine for about 4 weeks but I guess it was so restrictive that once it got a little dirty, it was too much for the furnace and caused all the problems. Go figure. Get a supposedly better air filter and it almost breaks my furnace! Lesson learned.
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Old 02-12-2011, 02:13 AM   #5
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Replaced thermostat but it is still changing set temp on its own!


When a furnace breaks, it is always the thermostat!! *sarcasm*
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Old 02-12-2011, 07:20 AM   #6
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Replaced thermostat but it is still changing set temp on its own!


If using a 1250 rated filter causes the rollout switch to trigger then this is a good indication that you either have to many dampers closed on your system, not enough return air (undersized return air duct) or undersized supply ducting, or a dirty heat exchanger or A coil.

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