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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 945
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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I have a Lennox furnace which has had flame sensors becoming

Customer Question

I have a Lennox furnace which has had flame sensors becoming very dirty three to four times in winter season, causing the furnace to need a cleaning of the sensor or a new one. I change my filters monthly, so what could be causing this?
JA: Did you check the furnace's filters?
Customer: I change them monthly
JA: Do you plan on doing the work yourself?
Customer: Never! I call Moore Heating who installed the furnace and they do annual maintenance in the fall, but I have to have at least one emergency service per year
JA: Anything else we should know to help you best?
Customer: What could be causing the flame sensor to foul so frequently?
Submitted: 9 months ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 9 months ago.

Hi I'm Brian and I'm here to help!

The most likely cause for this is poor combustion and an incorrect fuel/air ratio. Your tech should perform a full combustion analysis and make adjustments accordingly. When the flame is too oxidizing or carburizing, it is considered a 'dirty flame' and will coat your flame sensor with deposits. Causes for this are either too little/too much gas pressure at the burners or too little/too much air flow through the burners. This should have been adjusted at the original installation and checked every couple years for proper adjustment.

Let me know if you have further questions on this subject. Otherwise, please remember to rate before leaving (3 stars or higher please!). Bonuses are always appreciated! And remember, follow up questions about this topic are free even after rating. Just post a new reply on this same question and I'll be notified. Thanks for allowing me to help and thanks for using Just Answer!

Thank you,