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| We have a 5-6 year old Trane XR80 furnace. Intermittently it will exhibit the following behavior:
1. Thermostat calls for heat 2. Draft motor starts and runs for 15-20 sec. 3. "Click" is heard (presumably gas valve opening or ignitor) 4. Nothing happens (normally burners would light now) 5. Draft motor continues to run, then stops, starts again. On second (or rarely a third) attempt, burners do light and furnace runs normally. When I had a clean and check done last fall, I relayed this problem to the tech and he confidently said it was likely a dirty flame sensor. He cleaned the sensor with fine sandpaper and polished with steel wool. Reinserted and the furnance ran flawlessly for a couple months before the behavior returned sporadically. Furnce was inspected and flame sensor cleaned again that winter and reduced incident rate of problem, yet problem still occurred not more than 4-5 hours after tech had cleaned flame sensor. Now it's happening again...this morning twice in a row when the thermostat called for heat.
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Follow-Up Postings:
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- Posted by baldloonie (My Page) on Thu, Nov 1, 07 at 17:33
| Flame sensor would only be if the burners lit for about 6 seconds then when out. If they aren't lighting at all, could be no gas to the furnace, bad gas valve or bad board. |
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- Posted by deweymn (gunken07@yahoo.com) on Thu, Nov 1, 07 at 23:19
| Sounds like you have a hot surface ignitor problem. That is the unit that glows white hot and ignites the gas. The only time a flame sensor is activated is when either a pilot flame or flame from the actual burners heats it up. Was an ohm reading ever done on the hsi? Did a tech ever take a microamp reading of the flame sensor output? Is the flame sensor properly positioned in the flame? Is the crossover flame or the burner near the flame sensor clean? A low flame output near the flame sensor causes a lower reading of the flame sensor signal (microamps) which if not enough will cause the gas valve to close. Then a re-ignition sequence will start. 3 failures on a lot of units will cause a 1-3hr shut down. (lock out) How else will the furnace be able to tell you that something is not working properly? |
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| I had a similar problem with my Heil 5000 gas furnace. There was a pressure switch to detect positive pressure (i.e, the exhaust fan is operating) on the exhaust side of the fan. The switch was fed by a rubber hose. I would shut the furnace down and pull off this rubber hose. There was a small nipple and it would be clogged by debris. I just took a small piece of wire and cleaned it out. This worked for me. Good luck. |
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- Posted by bill(bwilliams1361@sbcglobal.net) onSun, Apr 17, 11 at 15:27
| replaced the ignitor, thermostat, filter. it would light up in the beginning it would run about an 1/2 hour then flame would go off and the blower would keep running. when we put in new thermostat it run a couple of times now it won't even light up. any suggestions? we are on a pension and can't afford to have someone out. please help. |
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