Question about Honeywell Electronic Programmable Heat/Cool Thermostat - CT3300A100 Heater

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Furnace not cycling properly

My furnace is set at 72, but my house is kept at about 44. I put a new thermostat on but I am having the same problems. The furnace will start going through its normal cycles for about an hour or so and the temp will start to rise to around the mid 50's, never the same temp. Then it will just stop cycling and go back down to the mid to low 40's, again never the same temp. Sometimes the furnace will turn on, on its own. Other times I have to flip the switch located on the furnace off then on to get it to cycle. The temp never reaches freezing levels but won't warm up enough either. The igniter is electric is electric working fine. The vents all seem to be working and I changed the filter but the old one wasn't to bad. How do I get the furnace to run long enough to heat up my house? Is there a setting on my furnace I need to adjust?

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  • dobsonj18 Jan 19, 2009

    All the grills are clear. I will try taking the filter out, thanks for the tip. Thwe furnace was installed in 2004. I just purchased the house 6 mths ago and I have never cleaned it, I will do so immediately. It doesn't look to bad but I will clean it anyway. The furnace is a Conquest 90, if that helps at all. Last night it ran for 3 1/2 hours without any problems. When I went to bed it quit working, I woke up cold! It is still running fine it just shutts off at random temps and won't turn back on without me manually doing so. Hopefully that helps you diagnose the problem. Let me know if there are any other questions I can answer to help you out with my problem. Thanks again for all your help.

  • dobsonj18 Jan 21, 2009

    I tried cleaning the flame sensor but it didn't work so I will replace it and see what happens. Thanks for the help, If you have any other suggestions that you think would help, that would be great.

  • Scott Magill May 11, 2010

    How old is the furnace? When was the last time it was cleaned? What does the back of blower motor like? Have you tried to take filter out? Have you checked the return grill in your house to make sure there is nothing in front of it blocking the air flow? Please give me some feed back and i can give you some other things to check.


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Sounds like the flame sensor needs to be replace. You can try cleaning it with steel wool. This will get you by for a little while.

Posted on Jan 20, 2009

  • Scott Magill Jan 22, 2009

    where are the vents located on top of the house or out the side? Is there any snow on the ground? If there is the vent has a screen in it so birds don't get in their the vent could be getting plugedup. Before you reset the furnace next time you should have a sight galass you can see a red light see how many times it blinks should be like two or three blinks fast then a pause the the blinks again. this red light should be on the control board then on one of the front panels should tell you what the problem. the pressure switch could be causing the problem the control board should tell you if thats what it is


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