Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence MECH-FLAME-SENSOR Error Fix: Dirty Flame Sensor Rod — Furnace Lights Then Shuts Off

Error code MECH-FLAME-SENSOR on the Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence means: Dirty Flame Sensor Rod — Furnace Lights Then Shuts Off. The furnace ignites and runs for 3-7 seconds, then the burners shut off and the ignition cycle repeats. This is the #1 Carrier furnace service call and is caused by carbon buildup on the flame sensor rod. The flame sensor is a thin metal rod positioned in the burner flame path — it conducts a tiny DC current (2-6 microamps) through the flame to the grounded burner assembly, proving to the control board that flame is present. When the rod is dirty, this current drops below the detection threshold. To fix: turn off the furnace power and gas. Locate the flame sensor — it's a thin metal rod mounted with a single 1/4" hex screw near the burner assembly (usually at the opposite end from the ignitor). Remove it, clean the metal rod with fine emery cloth, steel wool, or a Scotch-Brite pad until the metal is clean and shiny. Reinstall and test. This $0 repair takes 10 minutes and solves the problem in 90% of cases where the furnace lights then shuts off.

The most successful fix is "Clean the Flame Sensor Rod" (easy difficulty, ~10 minutes). Estimated DIY cost: $0-$10. HomeMD has 2 community-ranked fixes for this error.

This error is rated low severity. It is generally not urgent and can often be resolved with a simple DIY fix.

Yes — the top-ranked community fix ("Clean the Flame Sensor Rod") is rated easy difficulty and takes about 10 minutes. Tools needed: 1/4 inch hex driver or nut driver, Fine emery cloth or Scotch-Brite pad.

DIY cost: $0-$10. Professional repair typically costs $80-$120. Many homeowners save money by trying the top-ranked community fix first.

The Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence has 8 other known error codes, including: CODE-21 (Infinity Code 21 — Gas Heating Lockout), CODE-22 (Infinity Code 22 — Abnormal Flame-Proving Signal), CODE-23 (Infinity Code 23 — Pressure Switch Fault), CODE-24 (Infinity Code 24 — Secondary Voltage Fuse Blown), CODE-26 (Infinity Code 26 — Line Voltage Limit Circuit Open), and 3 more.

Error code MECH-FLAME-SENSOR also appears on 5 other Carrier models: 58STA090-1-16 90,000 BTU 80% AFUE Single-Stage Gas Furnace, Carrier 58SB0 Comfort 80 Single-Stage 80% AFUE Gas Furnace, Carrier 58STA/STX 80,000 BTU 80% AFUE Single-Stage Upflow Gas Furnace, Carrier 59TN6 Infinity 96 Two-Stage 96% AFUE Gas Furnace with Variable-Speed Blower, Carrier 59TP6A080E17 80,000 BTU 96% AFUE Two-Stage Gas Furnace with Variable-Speed Blower. The fix may vary by model, so check each model's specific page for tailored repair steps.