HVAC Error Codes by Brand

Quick answer: HVAC error codes by brand are not standardized — the same code means different things on Carrier, Trane, Lennox, Rheem, Goodman, York, and Daikin systems. Always look up the code with your specific brand and model number. For furnaces, the code legend is on the label inside the access panel door. For communicating systems (Carrier Infinity, Trane ComfortLink, Lennox iComfort), the thermostat display provides the most detailed error information.

The Service Call That Taught Me to Always Check the Brand First

A neighbor called me over to look at her furnace, which was displaying a blink code she had looked up online. “It says code 33 means a flame sensor error,” she said. “I already cleaned the flame sensor and it’s still doing it.” The furnace was a Trane. On a Carrier furnace, code 33 does indicate a limit or flame rollout issue — but on her Trane unit, the same blink pattern indicated a pressure switch fault. She had cleaned a perfectly functional flame sensor while the actual problem — a clogged condensate drain — went unaddressed.

That experience illustrates the most important rule about HVAC error codes by brand: the code number is meaningless without the brand and model. This guide organizes the most common error codes for the seven major HVAC brands sold in the United States — Carrier, Trane, Lennox, Rheem, Goodman, York, and Daikin — with their meanings, causes, and recommended solutions.

How to Find Your HVAC Brand’s Error Code List

Before looking up any error code online, locate the error code legend for your specific unit. For furnaces and air handlers, this is a label affixed to the inside of the access panel door — it lists every code the control board can generate and a brief description of each fault. This label is the authoritative source for your specific model and is more reliable than generic online code lists.

For the complete service manual — which includes all error codes, diagnostic flowcharts, component specifications, and wiring diagrams — search your brand name + model number + “service manual.” Most major HVAC manufacturers publish service manuals on their websites or through their dealer portals. The model number is on a data plate inside the unit’s access panel (furnaces and air handlers) or on the outdoor unit’s cabinet (heat pumps and condensing units).

For communicating HVAC systems — Carrier Infinity, Trane ComfortLink II, Lennox iComfort, Daikin One — the thermostat display and companion app provide the most detailed error information, including the specific component that triggered the fault and the recommended diagnostic steps.

The 5 Most Common HVAC Error Code Categories Across All Brands

1. Ignition and Flame Sensor Errors

Ignition and flame sensor errors appear across all furnace brands. The underlying fault is consistent — the furnace attempted to light the burner but failed to establish or confirm a flame — but the code numbers differ by brand. Carrier: 14 (ignition lockout), 34 (ignition proving failure — flame sensor). Trane: LED blink 4 (ignition failure). Lennox: E4 (ignition failure). Rheem: LED blink 4 (ignition failure). Goodman: LED blink 4 (ignition failure). The most common cause across all brands is a dirty flame sensor — clean with 0000 steel wool before assuming igniter failure.

2. Pressure Switch and Airflow Errors

Pressure switch errors indicate that the inducer motor is not creating sufficient draft, or that the pressure switch hose is cracked or blocked. Carrier: 22 (pressure switch stuck open), 31 (pressure switch stuck closed). Trane: LED blink 2 (pressure switch fault). Lennox: E1 (pressure switch fault), E2 (pressure switch stuck closed). Rheem: LED blink 2 (pressure switch fault). Goodman: LED blink 2 (pressure switch fault). On high-efficiency condensing furnaces, a clogged condensate drain is the most common cause of pressure switch errors across all brands.

3. Limit Switch and Overheating Errors

Limit switch errors indicate that the heat exchanger has overheated — caused by restricted airflow (dirty filter, closed vents, failed blower motor). Carrier: 13 (limit device lockout), 33 (limit or flame rollout switch open). Trane: LED blink 3 (limit switch open). Lennox: E3 (limit switch open). Rheem: LED blink 3 (limit switch open). Goodman: LED blink 3 (limit switch open). Replace the air filter first across all brands — this resolves the majority of limit switch errors.

4. Refrigerant Pressure Errors (Heat Pumps and AC)

Refrigerant pressure errors appear on heat pumps and air conditioning systems across all brands. Low pressure errors indicate a refrigerant leak or undercharge; high pressure errors indicate a blocked condenser or overcharge. All refrigerant pressure errors require a certified HVAC technician — EPA Section 608 certification is legally required for refrigerant handling. Carrier: LP (low pressure), HP (high pressure). Trane: 126 (low pressure), 127 (high pressure). Lennox: P1 (low pressure), P2 (high pressure). Rheem: LP (low pressure), HP (high pressure). Daikin: P1 (low pressure), P2 (high pressure).

5. Communication Errors (Communicating Systems)

Communication errors on communicating HVAC systems indicate that the indoor and outdoor units — or the thermostat and the air handler — cannot exchange data signals. Carrier Infinity: communication fault displayed on thermostat with specific component identification. Trane ComfortLink II: 179 (communication fault). Lennox iComfort: communication error with component identification. Daikin: U8 (communication error between indoor and outdoor units). Communication errors are diagnosed by checking the communication wiring between components and performing a system power reset.

HVAC Error Codes by Brand: Step-by-Step Reference

Step 1: Carrier HVAC Error Codes

Carrier furnaces use LED blink codes on the control board. The code legend is on the label inside the furnace door. Key Carrier furnace codes: 13 (limit device lockout — replace filter, check airflow), 14 (ignition lockout — check igniter and flame sensor), 22 (pressure switch stuck open — check inducer motor and flue), 24 (secondary voltage fuse blown — check for wiring short), 31 (pressure switch stuck closed — check pressure switch hose), 33 (limit or flame rollout switch open — replace filter, check heat exchanger), 34 (ignition proving failure — clean flame sensor). Carrier Infinity systems display alphanumeric codes on the Infinity thermostat with component-specific descriptions. For Carrier heat pumps and AC units, error codes are displayed on the Infinity thermostat or communicated via LED on the outdoor unit.

Step 2: Trane HVAC Error Codes

Trane furnaces use LED blink codes; Trane communicating systems (XL824, XL850, XL1050 thermostats with ComfortLink II) display numeric codes. Key Trane communicating system codes: 126 (low refrigerant pressure — technician required), 127 (high refrigerant pressure — technician required), 128 (discharge temperature fault — compressor overheating), 179 (communication fault — check wiring between components), 551 (defrost fault — heat pump defrost sensor or cycle failure). Trane furnace LED blink codes follow a similar pattern to other brands: 2 blinks (pressure switch), 3 blinks (limit switch), 4 blinks (ignition failure), 5 blinks (flame sensed without call for heat — check gas valve). Always verify with the label inside your specific Trane unit’s access panel.

Step 3: Lennox HVAC Error Codes

Lennox furnaces use alphanumeric LED codes (E1–E9) rather than blink counts, making them easier to read than blink-code systems. Key Lennox furnace codes: E1 (pressure switch fault — check inducer and condensate drain), E2 (pressure switch stuck closed — check pressure switch hose), E3 (limit switch open — replace filter, check airflow), E4 (ignition failure — check igniter and flame sensor), E5 (flame sensed without call for heat — check gas valve), E6 (rollout switch open — check heat exchanger), E7 (low flame signal — clean flame sensor), E8 (low inducer speed — check inducer motor). Lennox iComfort systems display codes through the iComfort thermostat and app with detailed component identification.

Step 4: Rheem and Goodman HVAC Error Codes

Rheem and Goodman furnaces use LED blink codes similar to Carrier. Rheem key codes: 2 blinks (pressure switch fault), 3 blinks (limit switch open — check filter), 4 blinks (ignition failure — check igniter and flame sensor), 5 blinks (flame sensed without call for heat), 6 blinks (115V power reversed or grounding fault), 7 blinks (gas valve circuit fault). Goodman key codes follow the same pattern as Rheem (Goodman and Rheem share similar control board architectures). For Rheem and Goodman heat pumps, error codes are displayed on the outdoor unit’s LED or on the thermostat. Always verify with the label inside the access panel — Rheem and Goodman have multiple product lines with different code assignments.

Step 5: York and Daikin HVAC Error Codes

York furnaces use LED blink codes similar to other brands. Key York codes: 2 blinks (pressure switch fault), 3 blinks (limit switch open), 4 blinks (ignition failure), 5 blinks (flame sensed without call for heat), 6 blinks (115V power fault). York heat pumps and AC units display codes on the thermostat or via LED on the outdoor unit. Daikin systems — particularly Daikin mini splits and VRV commercial systems — use alphanumeric codes: E1 (indoor PCB fault), E3 (outdoor fan motor fault), E4 (compressor discharge temperature fault), E5 (compressor overload), E6 (compressor lock), E7 (outdoor fan motor fault), U0 (refrigerant shortage — technician required), U2 (low voltage fault), U4 (communication fault between indoor and outdoor units), U8 (communication fault — outdoor unit). Daikin’s error code system is among the most comprehensive in the industry, with codes covering over 50 distinct fault conditions.

Frequently Asked Questions About HVAC Error Codes by Brand

Are HVAC error codes the same across all brands?

No — HVAC error codes are not standardized across brands. The same code number can mean entirely different things on different brands. Code 33 on a Carrier furnace indicates a limit or rollout switch fault; on a Trane system, the same blink pattern may indicate a different fault. Always look up the code with your specific brand name and model number — the label inside the access panel door is the most reliable reference.

What do Carrier furnace error codes mean?

Key Carrier furnace codes: 13 (limit device lockout — check filter), 14 (ignition lockout — check igniter and flame sensor), 22 (pressure switch stuck open — check inducer and flue), 31 (pressure switch stuck closed — check hose), 33 (limit or rollout switch open — check filter and heat exchanger), 34 (ignition proving failure — clean flame sensor). The complete code legend is on the label inside the furnace door.

What do Trane HVAC error codes mean?

Trane communicating system codes: 126 (low refrigerant pressure), 127 (high refrigerant pressure), 128 (discharge temperature fault), 179 (communication fault), 551 (defrost fault). Trane furnace LED blink codes: 2 blinks (pressure switch), 3 blinks (limit switch), 4 blinks (ignition failure), 5 blinks (flame without call for heat). Always verify with the label inside your specific Trane unit.

What do Lennox HVAC error codes mean?

Lennox furnace alphanumeric codes: E1 (pressure switch fault), E2 (pressure switch stuck closed), E3 (limit switch open — check filter), E4 (ignition failure), E5 (flame without call for heat), E6 (rollout switch open), E7 (low flame signal — clean sensor), E8 (low inducer speed). Lennox iComfort systems provide more detailed codes through the thermostat and app.

How do I find my HVAC brand’s error code list?

Check the label inside the unit’s access panel door first — it lists all codes for your specific model. For the complete service manual, search your brand name + model number + “service manual.” For communicating systems (Carrier Infinity, Trane ComfortLink, Lennox iComfort, Daikin One), the thermostat display and companion app provide the most detailed error information with component-specific descriptions.

HVAC Error Code Quick Reference by Brand

The table below summarizes the most common error codes for major HVAC brands in the United States. Codes are approximate — always verify with the label inside your specific unit’s access panel.

Note: This table is a general reference only. Error codes vary between product lines and model years within each brand. Always verify codes with the label inside your specific unit’s access panel or the manufacturer’s service manual for your model number. Refrigerant pressure errors (LP, HP, P1, P2, U0, 126, 127) require a certified HVAC technician — EPA Section 608 certification is legally required for refrigerant handling.

Conclusion: Brand First, Code Second

The neighbor who cleaned a perfectly functional flame sensor because she looked up a generic “code 33” result online lost an hour of work and still had a clogged condensate drain. The lesson is simple: the brand and model number come before the error code in every HVAC diagnosis. The label inside the access panel door is always the first reference — not a generic online list.

HVAC error codes by brand follow consistent fault categories — ignition, pressure switch, limit switch, refrigerant pressure, communication — but the specific code numbers and letters assigned to each fault vary significantly across Carrier, Trane, Lennox, Rheem, Goodman, York, and Daikin. Understanding the fault categories allows you to make an accurate first assessment; the brand-specific code confirms the diagnosis.

For communicating HVAC systems — Carrier Infinity, Trane ComfortLink II, Lennox iComfort, Daikin One — the thermostat display and companion app provide the most detailed and accurate error information available, often identifying the specific failed component and the recommended diagnostic steps. If your system has a communicating thermostat, use it as your primary diagnostic tool before consulting any external reference.

Sources

• U.S. Environmental Protection Agency (EPA) — Section 608 Refrigerant Management Regulations. Available at: www.epa.gov/section608
• North American Technician Excellence (NATE) — HVAC Technician Certification Standards by Equipment Type. Available at: www.natex.org
• Air-Conditioning, Heating, and Refrigeration Institute (AHRI) — Industry Standards for Residential and Commercial HVAC Equipment. Available at: www.ahrinet.org
• U.S. Department of Energy (DOE) — HVAC Equipment Efficiency Standards and Technology Overview. Available at: www.energy.gov
• Consumer Reports — HVAC Brand Reliability and Repair Cost Survey, 2023. Available at: www.consumerreports.org