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Thermostat not running furnace properly

Had the problem of furnace running for a few minutes and shutting off at the end of last heating season. figured it was the Thermostat and replaced it with a Honeywell CT87K4446 and problem still exists? Replaced the Photo Eye with a Honeywell C554A1463 Cadmium Sulfide Flame Sensor and the Mechanical Controller with a new Honeywell R8184G4009 International Oil Burner Control . Problem still exists? The furnace will run for a few minutes and shut off? Sometimes fan comes on sometimes not depending on if it ran long enough to trigger the heat switch. If you turn the thermostat up and call for heat everything works as it should. If you set it and let it call for heat on its own, you will hear the thermostat click to call for heat and shortly after that it clicks off. As if maybe the thermostat is generating enough heat within itself from just calling for heat and is in turn is shutting off before the fan runs? Do I need to put a relay in between the thermostat and controller so this load at the thermostat will not be present?

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  • 210 Answers

Assuming that particular thermostat has a common mercury switch, the wiring behind or just inside the unit may be causing a strong enough magnetic field to throw off the balance of the mercury (liquid metal). The same scenario could be caused by other wiring or devices near the thermostat.
To test this theory, hold a compass as near as possible to the thermostat and wait it to come on automatically. If the needle moves when the switch engages, the magnetic field is strong enough the throw the balance off.


When tucking-in the wires for the thermostat, avoid winding the wires in a spiral or wrapping them around anything. An active current through wrapped or winding wires will create an electromagnetic field.

Posted on Oct 29, 2012

  • donitarenzo7
    donitarenzo7 Oct 29, 2012

    I know what You are talking about, but that isn't the case here. Wires barely reach.

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heatman101
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SOURCE: Burner ignites and goes out (Goodman Gas-fired furnace)

Hi,
The problem you have is water in the exhaust pipe.
Check to see if the pipe has sagged anywhere or if there is a trap in the line.
If you hear gurgling then it is definetly water....
Some times can be hard to find, even a pipe 1/4 full will cause problems. They are very sensitive to flue problems.
Make sure that the flue pipe either runs back to the furnace or out to the outside, a continuos slope either way witha high spot in the middle.
Also check the bottom drain of the blower if it has one, have had them plug and trap water also..

I hope that this will help you to solve your problem!

Thanks for using Fixya!!

Heatman101

Posted on Dec 24, 2009

  • 221 Answers

SOURCE: furnace ignites when thermostat calls for heat,

You don't say if the blower is coming on, no blower would cause the limit to open. By the way, the limit is internal and auto-reset, not the manual reset roll out switches on the burner assembly.

Posted on Jan 11, 2010

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Check the flame sensor and/or the grounding from the burner ot the ignition control....it is not sensing the flame...

Here is a tip that will help you try to figure out why your furnace is not working.

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Hello Genna,
I am not a furnace guy but I may be able to give you a few ideas of things to diagnose the problem and get it resolved. First off, I assume you have a thermostat that you use to to turn your heat on. If it is a generic ( meaning : non programmable model) then you should be able to try this simple test. Remove the cover ( typically they snap on) around the thermostat so you can see the control mechanism inside. You should see few skinny wires ( similar to those used on a telephone wire) solid copper in various colors.. When you rotate the dial on your thermostat to call for heat, there is a small glass vial that has a drop of mercury ( which is electrically conductive) in it that makes contact and shorts two control wires together ad that is what calls for heat on your furnace. When the temp inside the room where the thermostat is reaches the tempertaure you requested, the bimetal mechanism either contracts or expands to reposition that glass vial to shift the mercury off the contacts and your furnace shuts off... That is the basics behind how your thermostat and furnace work ( generally speaking) If you can identify the two wires inside the thermosat that are shorted together when that vial of mercury shorts them inside it.. you can temproarily unhook them ( they are low voltage.. normally 24 Volts or less) so no worries about getting ashock or anything.. and short them together for a minute or two.. by doing that... your furnace should turn on and heat should flow.... Once you start your furnace this way.. unhook these two wires and your furnace should shut down .. It may take a minute or two ( depending on the control for it) If it doesn't..then your problem is on the furnace side and you may need to get the furnace control system serviced or replaced.. if it does shut down, then your problem is your thermostat and thats a simple replacement.. Also.. make sure the thermostat was properly leveled on its base.. The position of the thermostat ( meaning level) will dictate when that mercury makes contact and your furnace switches on.. OK..I tried to explain the works of this to you but here is a link to a Honeywell site that explains it in simpler terms.. The part about shorting the two wires together and then opening them will aid you in identifying where the problem actually is.. here is the link: http://homerepair.about.com/od/heatingcoolingrepair/ss/thermostat.htm

Hope this helps you more than confuses you..
Regards

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