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My furnace will not reach the desired house temperature in one cycle. It will run for several minutes, shut off, and repeat. It eventually reaches the desired temp but it take a long time and I feel it may be a symptom of a larger, looming problem. I have replaced the filter, and did a spot check on cold return ductwork to verify it is clean. I have also installed a new thermostat with no change. My next steps are to remove and inspect the blower, inspect and clean the flame sensor, and/or wire the blower to run faster. Any suggestions would be appreciated.

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There are a few different reasons for short cycling of a furnace.
1. Inadequate air flow. Not enough air moving through the furnace can cause it to overheat and trip the high temperature limit switch.
check to see that all registers are open and returns are not blocked.
2 Improper heat anticipator setting on thermostat. Some thermostats have a heat anticipator and too low of a setting can cause short cycling.

4 Partially blocked drain hoses. If the condensate backs up into the furnace it can shut the flame off and then when the condensate drains the furnace starts again. Check all drain hoses to make sure they are clear.
These are just some of the possible reasons for short cycling .
Hope this helps.

Posted on Dec 26, 2013

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  • Lee Lee
    Lee Lee Dec 26, 2013

    Thank you for your response. My vents are open and clean, as are my return lines. I just performed an external check on my drains from the furnace. I could disassemble one and see the PVC was clean and I poured water down the other and it came out promptly on the discharge. Is this suffucient or do I need to open the furnace and check the drain lines on the inside? One drain line is off the condensate trap near the service panel and will be easy to access. The second is higher up, near the back, presumably from the heat exchanger area. Both are candidate problems? When you point me to the heat anticipator on the thermostat do you mean my wall thermostat or a thermostat inside the furnace. Thank you again and sorry for so many questions.

  • Lee Lee
    Lee Lee Dec 26, 2013

    I educated myself on the thermostat anticipator rate and know to what you refer. A few weeks ago, I replaced my thermostat in hopes a faulty thermostat was causing the cycling. That was not the solution. I have a Honeywell RTH2300B. It has a preset for heating cycle rate and I have it set according to the manual. It does not allow any further adjustment. The heating cycle rate I have selected is for a hot water or high efficiency furnace.

  • Lee Lee
    Lee Lee Dec 27, 2013

    I removed the panels and observed the furnace as it shut down. The flame burns for several minutes, a good blue flame. Eventually, the flame is lost. The unit begisn clicking, I assume an electronic ignition attempt is making the clicking sound. The hot surface igniter and/or flame sensor glows and (my memory is weak) I think there is a small blue flame at the igniter/sensor. It runs through the clicking process for five occasions before shutting down. The combustion air blowers stops and the circulating blower continues for about 30 seconds. I found a manual online with error codes. The code is 6 + 2 flashes. The manual says Soft Lockout: Indicates last failure was flame sense lost during run. Possible causes are: Flame sense rod contaminated or in incorrect position. Pilot burner located in incorrect position. Cycling, pressure switch Condensate drain blocked Pressure switches operation, tubing, and wiring. I am not sure what all of that means. I think my igniter and sensor are good as the furnace always comes on when demanded and always runs for several minutes. I do not know what the pressure switch portion is telling me. I suspect the drain issue is the problem. I hope that if I remove the hoses for the vent pipe drain and transition box drains, that I will see an obvious obstruction. I will also check the condensate trap, as both of the above drains flow through the trap. The trap does have CO2 warnings. If anyone has any ideas on the drains, I would be appreciative. Or, if you feel I am underestimating the likelihood of the igniter and sensor, I'd like to know that. Thank you for reading this long paragraph.

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Therinnaiguy
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SOURCE: BLOWER CONTINUES TO BLOW COLD AIR AFTER REACHING DESIRED TEMP.

There is a little switch on the circuit board. Look closely at the wiring diagram and it will indicate which switch to adjust. If not, review the operating manual for details.

Posted on Nov 25, 2008

mrgrzz
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SOURCE: furnace blower not working how it should

first off buy yourself a honeywell stat, in my personal opinion lux stats are garbage, I have run into so many that are bad stats !!! but as far as your fan not shuting down, sounds to me like your fan center on your circuit board is bad and will not shut down the fan when needed, you will have to replace the circuit board, as the fan center is a part of the whole of the circuit board, hope that helps

Posted on Jan 20, 2009

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SOURCE: once temperature is reached the burner still trys

Need a thermocouple it sounds like to me.

Posted on Apr 17, 2009

Therinnaiguy
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SOURCE: Rheem RHQA Heater:Blower works but no heat.

Is there a setting on the thermostat for Auto or Fan? If so, make sure it is in the Auto setting. You will have a contactor that turns on the elements and a relay for the fan. Follow the wiring diagram to see which relay energizes the fan then unplug it to see if the fan stops.

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SOURCE: XE 90 gas furnace--furnace will light and run for

hi check out the temp rise and fall on the fan control see if he has left the blower in the summer swich postion where it runs all the time

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