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CODE-21

Carrier · Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence

Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence CODE-21 Error Fix: Infinity Code 21 — Gas Heating Lockout

The Infinity System Control displays "Code 21" indicating the gas furnace has entered ignition lockout. The furnace attempted to ignite multiple times and failed. This is the Infinity equivalent of LED Blink Code 1 on non-communicating furnaces. The Infinity Control may display additional detail about the specific failure stage. Common causes: dirty flame sensor, failed ignitor, no gas supply, or gas valve failure. To reset: from the Infinity Control thermostat, navigate to the Service/Diagnostics menu and clear the fault, or cycle the furnace power. If lockout recurs, clean the flame sensor rod as a first step — this resolves the problem in the majority of cases. The Infinity Control stores a fault history that an HVAC technician can access for diagnosis.

High severity2 fixes available✨ Free fix available

Quick Answer

Error CODE-21 on the Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence means: Infinity Code 21 — Gas Heating Lockout. The top-ranked community fix is “Replace the Ignitor Assembly” (medium difficulty, ~45 min, DIY cost: $15-$25). 2 community-ranked fixes available below.

Published February 2026 · 2 fixes · furnace

Content is based on manufacturer service documentation, community repair experience, and OEM technical bulletins. Always verify with your owner's manual.Learn about our editorial standards.

When to Call a Professional

While many furnace repairs can be done safely at home, consider hiring a qualified technician if:

This is a high severity error — continued use may cause damage or a safety hazard
The repair involves electrical wiring, gas lines, or refrigerant
You've tried the top-ranked fix and the error persists
You smell gas, see sparking, or notice water leaking
The repair requires specialized tools you don't have
Your appliance is still under manufacturer warranty

Average professional repair cost for this issue: $150-$250.

Other Carrier Models with Error CODE-21

Carrier 59TN6 Infinity 96 Two-Stage 96% AFUE Gas Furnace with Variable-Speed Blower

furnace · 2 fixes

Other Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence Error Codes

CODE-22

Infinity Code 22 — Abnormal Flame-Proving Signal

2 fixes

CODE-23

Infinity Code 23 — Pressure Switch Fault

2 fixes

CODE-24

Infinity Code 24 — Secondary Voltage Fuse Blown

2 fixes

CODE-26

Infinity Code 26 — Line Voltage Limit Circuit Open

2 fixes

CODE-41

Infinity Code 41 — Blower Motor Fault

2 fixes

CODE-42

Infinity Code 42 — Inducer Motor Fault

2 fixes

CODE-43

Infinity Code 43 — Low Flame Signal / Dirty Flame Sensor

2 fixes

CODE-44

Infinity Code 44 — Blower Calibration Fault

2 fixes

People Also Ask About Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence Error CODE-21

What does error code CODE-21 mean on a Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence?

Error code CODE-21 on the Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence means: Infinity Code 21 — Gas Heating Lockout. The Infinity System Control displays "Code 21" indicating the gas furnace has entered ignition lockout. The furnace attempted to ignite multiple times and failed. This is the Infinity equivalent of LED Blink Code 1 on non-communicating furnaces. The Infinity Control may display additional detail about the specific failure stage. Common causes: dirty flame sensor, failed ignitor, no gas supply, or gas valve failure. To reset: from the Infinity Control thermostat, navigate to the Service/Diagnostics menu and clear the fault, or cycle the furnace power. If lockout recurs, clean the flame sensor rod as a first step — this resolves the problem in the majority of cases. The Infinity Control stores a fault history that an HVAC technician can access for diagnosis.

How do I fix error code CODE-21 on my Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence?

The most successful fix is "Replace the Ignitor Assembly" (medium difficulty, ~45 minutes). Estimated DIY cost: $15-$25. HomeMD has 2 community-ranked fixes for this error.

Is error code CODE-21 on a Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence serious?

This error is rated high severity. You should address it promptly — continued use could cause damage or safety concerns.

Can I fix Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence error CODE-21 myself?

Yes — the top-ranked community fix ("Replace the Ignitor Assembly") is rated medium difficulty and takes about 45 minutes. Tools needed: T20 Torx screwdriver, Multimeter (optional).

How much does it cost to repair Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence error CODE-21?

DIY cost: $15-$25. Professional repair typically costs $150-$250. Many homeowners save money by trying the top-ranked community fix first.

What other error codes does the Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence have?

The Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence has 8 other known error codes, including: 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), CODE-41 (Infinity Code 41 — Blower Motor Fault), and 3 more.

Which other Carrier models have the CODE-21 error?

Error code CODE-21 also appears on 1 other Carrier model: Carrier 59TN6 Infinity 96 Two-Stage 96% AFUE Gas Furnace with Variable-Speed Blower. The fix may vary by model, so check each model's specific page for tailored repair steps.

What other error codes does the Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence have?

The Carrier Carrier 59MN7 Infinity 98 Modulating 98.5% AFUE Gas Furnace with Greenspeed Intelligence has 8 other known error codes:

CODE-22 — Infinity Code 22 — Abnormal Flame-Proving Signal (2 fixes)
CODE-23 — Infinity Code 23 — Pressure Switch Fault (2 fixes)
CODE-24 — Infinity Code 24 — Secondary Voltage Fuse Blown (2 fixes)
CODE-26 — Infinity Code 26 — Line Voltage Limit Circuit Open (2 fixes)
CODE-41 — Infinity Code 41 — Blower Motor Fault (2 fixes)
CODE-42 — Infinity Code 42 — Inducer Motor Fault (2 fixes)
CODE-43 — Infinity Code 43 — Low Flame Signal / Dirty Flame Sensor (2 fixes)
CODE-44 — Infinity Code 44 — Blower Calibration Fault (2 fixes)

Which other Carrier models have the CODE-21 error?

Error code CODE-21 also appears on 1 other Carrier model:

Carrier 59TN6 Infinity 96 Two-Stage 96% AFUE Gas Furnace with Variable-Speed Blower (furnace) · 2 fixes

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