Have a Goodman GMT115-5B Natural Gas. Burners fire and blower comes on. If it has run for a longer period (not too long in my opinion), burner cycles on and off while blower is still running. Burner will ignite burn for 45-60 seconds and shut off then cycle back on again. Cycle will continue to repeat until thermostat reaches temp. Any thoughts?

Air filter dirty, gas pressure to high, return or supply registars closed. Or a week limit.

If the circuit board has a diagnostic LED, it will provide clues.

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Originally Posted by novicehvac

Have a Goodman GMT115-5B Natural Gas. Burners fire and blower comes on. If it has run for a longer period of time (not too long in my opinion), burner cycles on and off while blower is still running. Burner will ignite burn for 45-60 seconds and shut off then cycle back on again. Cycle will continue to repeat untill thermostat reaches temp. Any thoughts?

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Now, the burners come on and fire for 12-14 second then shut off, and cycle repeats. I have checked and indicator light is not flashing, no error codes are showing.

Thoughts?

Could be the limit switch or the flame sencer

Try bypassing the thermostat to see if cycle is sustained. Connect "R" and "W" circuits together, either at thermostat location or at furnace.

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Originally Posted by Joshdta

could be the limit switch or the flame sencer

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Cleaned the flame sensor, changed the filter, by-passed the stat. No change in propblem. Which limit switch and can I check it myself?

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