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coolman1973, Hvac tech and Mechanic
Category: HVAC
Satisfied Customers: 334
Experience:  15 yrs field exp/5yrs supervisingexp/ Nate and Epa cert.
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I have an Air Ease Ultra SX 80 furnace that is 12 years old.

Customer Question

I have an Air Ease Ultra SX 80 furnace that is 12 years old. The T-stat calls for heat, the HSI(hot start igniter) gets yellow hot, the pilot light starts burning, the FS(flame sensor) gets red hot, and then the main burners ignite. This takes about 20 seconds. However the main burners only run about 2 minutes to 5 minutes and then shut off, they restart in about 20 seconds after the HSI, pilot, and FS rerun their cycle. This will usually continue until the T-stat reaches its setting. However sometimes the main burners cycle on and off two, three or four times and then on the next cycle they do not reignite. The house gets cold and the induction fan runs, the pilot burns, FS, and HSI are all red/yellow hot. It runs in this condition for hours. Only when I shut off the main furnace switch and turn it back on, everything seems to work again for awhile(2-3 days), then problem reappears. What is wrong??
Submitted: 8 years ago.
Category: HVAC
Expert:  coolman1973 replied 8 years ago.
Ur flame sensor should not come onto play until the burners light. Its there to sense flame so ur gas valve doesnt keep pumping gas into the burners without ignition.
coolman1973, Hvac tech and Mechanic
Category: HVAC
Satisfied Customers: 334
Experience: 15 yrs field exp/5yrs supervisingexp/ Nate and Epa cert.
coolman1973 and 2 other HVAC Specialists are ready to help you
Customer: replied 8 years ago.

I do not think your answer is correct. My FS(flame sensor) gets electrically excited within seconds on a cold startup...about 4 volts going through it when you put a low voltage tester on it. The FS sets above the HSI(hot start igniter) and in front of the pilot lighter mouth. In fact the the pilot light flame lights off the HSI in about 10 seconds, while the FS gets "excited" in about 4 seconds. Maybe from the heat from the HSI??

Then the main burners light in about 15 - 20 seconds.

I just put in a new FS/HSI combo unit...bought late last year for $55.00...and so far so good. It is still cycling the main burners on and off, about 6 - 8 seconds off and 2 - 6 minutes on. As long as they keep coming back on until T-stat is satisfied!! Will know for sure in 2 - 3 days.

Customer: replied 8 years ago.

well coolman 1973, I will accept your answer so you can get paid. if I find out that the burners are supposed to cycle on/off...then everything is cool. if they are not supposed to..well, time to look for bad rollout switch, thermal limit switch,etc..

Merry Christmas fromCustomer


Expert:  Ronald replied 8 years ago.
Is there a rack of burners with a flame sensor at the end? If the sensor is faulty, the control board will shut doun the fuel flow and run the blow for a few minutes to clear the area of any raw gas and then retry. After a few retries the board will assume there is an error and for safety will shut down everything but usually leave the blower running to again clear any raw gas. The sensor is at the last burner, opposite side from the pilot assembly.