Furnace Cycling too Often House Stays Cold


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Old 11-06-13, 10:09 AM
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Furnace Cycling too Often House Stays Cold

We have recently bought a single level condo which has the furnace room located at the center of the house. Since it has just recently started to cool off outside we have been using the furnace more often and noticed that it was doing a very poor job of keeping the house warm and it will cycle on and off constantly. I first thought this was an issue with the thermostat itself so I replaced the old slider style thermostat yesterday with a new Honeywell touch screen thermostat. This did not fix the issue, the flame in the furnace unit seems to turn on for no longer than 15 to 30 seconds at a time at which point the fan sometimes is on and sometimes is off and will run and blow air through the house but with the flames being off it will not heat much. I have set the thermostat to 72 and the temperature reads 72. I have just tried setting the temperature to 90 to see if the flame will run longer but the furnace will not turn on at all. Any idea on where I should start the trouble shooting? If you need further information I will do my best to get you the answers.
 
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Old 11-06-13, 11:51 AM
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Brand and model of furnace will help answer questions. Jumpering red to white at the furnace will tell you if there is a wiring or stat problem. Just make sure to isolate any wires that you take loose so they don't touch the cabinet.
 
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Old 11-06-13, 01:52 PM
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I know that it is a Carrier furnace, I will have to wait till I get home to get you the model number. The furnace was recently replaced though I don't believe it's older than 1-2 years but I could be wrong. As far as the wires go, what am I looking for when I jump the Red and White together is there something I should check for in particular when I do this? Thanks.
 
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Old 11-06-13, 02:13 PM
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You should be able to see a low voltage wire going to the furnace that will have 4 or 5 wires inside a brown shielding. Looking at your board will allow you to see where R and W connect. Using a jump wire to short these two together should activate the heat mode. If it doesn't, it's internal to the furnace. If it does work, it would be external to wiring or stat. Note, you will probably have to make sure the door switch is manually pushed in, in order to do this test.
 
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Old 11-06-13, 02:35 PM
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Ok I will try to do these steps and record exactly everything that happens this evening and get it up on this forum, something tells me the wiring should be ok though since I can get the furnace and burners to come on and I can get the AC to come on. I just can't get the flames to stay on anywhere long enough to do any heating 15-30 seconds, and once it does the cycling of on and off of the burners I sometimes can't get the furnace to come on at all after raising the temperature. Update on the burners: the furnace did finally kick on after being set to 90 degrees and the burners kept burning for a while even after the heat was turned back down to 80 degrees. Not sure why that time delay is happening, from what I understand the furnace should come on the instant the temperature setting is turned up above the current temperature reading on the thermostat should it not?
 
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Old 11-06-13, 03:18 PM
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No older than your furnace is, you should see LED error codes. Bypassing the obvious is the first step. Observe sequence of start up. Should be inducer motor, pressure switch making, ignition trying and gas valve opening. After that it comes down to flame sensor or high limit.....IF there is not a faulty board.
 
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Old 11-06-13, 06:27 PM
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Pictures of the Furnace

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Old 11-06-13, 06:36 PM
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With the furnace being off I turned up the heat to 73 from 72. The furnace started "warming up" the heater pilot or coil turned on till it was glowing and the gas valve opened, we had flame for about 5 seconds, flame went out, the process repeated itself 2 more times, on the fourth try the flame turned on and stayed on for a prolonged period of time and the fan started blowing. I turned the heat down from 73 to 72 and the flames turned off as the fan kept blowing air. The part that should not be happening I'm guessing is the repeated flame on for 5 seconds and back off before things get going, other than that operation seems likeit is normal? I looked at the LED light signals and finally figured out what they were doing, when the flame goes out after five seconds or while the fan is blowing and there is not flame the LED's blink 3 short blinks and 4 long blinks which reffers you to code 34 on the label as pictured. I'm assuming it's safe to say I should try the recommended steps in order? Not sure where the sensor is located though suppose I should start taking it apart...any considerations before I proceed to follow the recommended steps? Thank You!
 
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Old 11-06-13, 07:16 PM
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If you leave the closet doors open --- does the furnace seem to operate correctly ?

It looks as though your gas furnace and gas water heater are located in a closet with solid doors ( not louvered ). It also appears those appliances don't seem to have enough combustion air once those doors are shut. Without enough combustion air for those appliances there could be backdrafting from the exhaust flues and possibly have flame suckout happening on the furnace and/or water heater.
 
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Old 11-06-13, 08:48 PM
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There is a pretty good size gap at the bottom of the doors and when I did my last test the doors were open the entire time and it still operated just as I described below.
 
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Old 11-06-13, 11:23 PM
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Clean the flame sensor.

It's a metal rod, most likely on the opposite side of the igniter.
 
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Old 11-07-13, 07:42 AM
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Any idea how often this process might need to be done? Is this usually the cause of the problems I'm having here? I guess if cleaning the sensor won't work, if I can find and get to it since the igniter is on the accessible side of the furnace , then the only other step I feel I have the knowledge to check is the grounding of the unit. The remaining possible issues I'm not sure how to check for:

- Proper flame sense microamps(.5ma DC min)
- Low inlet gas pressure
Is there a manual valve that might not be opened all the way?
- Inadequate flame carryover or rough ignition.

Are any of the steps above something I can't take care of myself? I can get an ammeter...but how to check proper gas inlet pressure beats me...
 
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Old 11-07-13, 07:07 PM
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Problem Fixed

The issue in fact did lie in the Flame Sensor, took the burner heads off and cleaned those while I was at it. Used a regular sink sponge green rough end to clean up the sensor rod. In the process decided to check the filter and found it to be rediculously dirty, probably an inch of dust built up on it. New filter, clean sensor and the burners kick on and stay on and I can actually feel the airflow from the vents, thanks everyone for your input probably saved a ton of money by not calling HVAC company
 
 

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