Lennox error codes
51 documented codes with ranked causes, repair costs, and step-by-step guidance.
Lennox air conditioner code chart (2) Lennox heat pump code chart (15) Lennox furnace code chart (34)
Lennox Air Conditioner — Frozen evaporator coil Lennox AC Frozen Evaporator Coil: Causes, Fixes & Costs Why a Lennox AC evaporator coil freezes: low airflow, low refrigerant, blower or metering faults. Safe thaw steps, technician fixes and US repair costs. Lennox Air Conditioner — Not cooling Lennox AC Not Cooling: Causes, Fixes & Repair Costs Lennox AC not cooling? Learn the likely causes, from dirty filters and capacitors to refrigerant leaks, safe fixes and honest US repair costs. Lennox Heat Pump — Runs constantly Lennox Heat Pump Runs Constantly: Causes, Fixes & Costs Lennox heat pump running nonstop? Learn the causes (low charge, dirty coils, stuck contactor, sizing), safe checks, and repair costs from $0 to $3,000. Lennox Heat Pump — Flashing light Lennox Heat Pump Flashing Light: Meaning, Causes & Fixes Lennox heat pump flashing light explained: what the board LED means, likely causes like pressure switch or sensor faults, safe checks, and repair costs. Lennox Heat Pump — Loud noise Lennox Heat Pump Loud Noise: Causes, Fixes & Costs Lennox heat pump making loud noises? Learn what each sound means, likely causes from fan to compressor, safe checks, and repair costs from $0 to $2,500+. Lennox Heat Pump — Won't turn on Lennox Heat Pump Won't Turn On: Causes, Fixes & Costs Lennox heat pump won't turn on? Learn the likely causes (power, thermostat, low voltage, board, float switch), safe fixes and US repair costs. Lennox Heat Pump — Compressor not running Lennox Heat Pump Compressor Not Running: Causes & Fixes Lennox heat pump compressor not running? Learn the causes (capacitor, contactor, lockout, controls), safe checks, and repair costs from $0 to $3,500+. Lennox Heat Pump — Breaker keeps tripping Lennox Heat Pump Breaker Keeps Tripping: Causes & Fixes Why a Lennox heat pump keeps tripping its breaker: shorted compressor, failed capacitor, fan motor or wiring faults, plus safe checks and repair costs. Lennox Heat Pump — Short cycling Lennox Heat Pump Short Cycling: Causes, Fixes & Costs Why a Lennox heat pump short cycles: thermostat, airflow, refrigerant charge, pressure switches and oversizing. Safe checks, pro fixes and $0–$2,500+ costs. Lennox Heat Pump — Blowing cold air in heat mode Lennox Heat Pump Blowing Cold Air in Heat Mode: Fixes Lennox heat pump blowing cold air on heat? Learn the causes (defrost, reversing valve, low charge), safe checks, fixes and typical repair costs. Lennox Heat Pump — Outdoor fan not spinning Lennox Heat Pump Outdoor Fan Not Spinning: Causes & Fixes Lennox heat pump outdoor fan not spinning? Learn the causes (capacitor, motor, contactor, defrost board), safe checks, and repair costs from $0 to $900. Lennox Heat Pump — Auxiliary heat on constantly Lennox Heat Pump Aux Heat On Constantly: Causes & Fixes Why a Lennox heat pump runs auxiliary heat nonstop: thermostat setup, low charge, sensor or relay faults. Safe checks, pro fixes and repair costs explained. Lennox Heat Pump — Stuck in defrost mode Lennox Heat Pump Stuck in Defrost Mode: Causes & Fixes Lennox heat pump stuck in defrost? Learn the causes (defrost board, sensor, reversing valve, relay), safe checks, and repair costs from $0 to $1,500+. Lennox Heat Pump — Frozen and not defrosting Lennox Heat Pump Frozen and Not Defrosting: Fixes & Cost Lennox heat pump iced over and not defrosting? Learn the causes (water drips, defrost sensor, board, reversing valve), safe checks, and repair costs. Lennox Heat Pump — Ice on outdoor unit Lennox Heat Pump Ice on Outdoor Unit: Causes & Fixes Ice on your Lennox heat pump's outdoor unit? Learn normal frost vs. problem icing, the likely causes, safe checks, and repair costs from $0 to $3,000+. Lennox Heat Pump — Not cooling Lennox Heat Pump Not Cooling: Causes, Fixes & Costs Lennox heat pump not cooling? Ranked causes like reversing valve, capacitor, low refrigerant and dirty coils, safe checks, and honest repair costs. Lennox Heat Pump — Not heating Lennox Heat Pump Not Heating: Causes, Fixes & Costs Lennox heat pump not heating? Causes like thermostat setup, defrost, low refrigerant or stuck reversing valve, safe checks, and repair costs. Lennox Furnace — Pressure switch stuck open Lennox Furnace Pressure Switch Stuck Open: Fixes & Cost Lennox furnace pressure switch stuck open: causes from blocked vents to a failing inducer, safe DIY checks, pro fixes, and real US repair costs. Lennox Furnace — Runs constantly but not enough heat Lennox Furnace Runs Constantly But Not Enough Heat Lennox furnace runs nonstop but can't keep up: dirty filter, undersized ducts, flame issues & more. DIY checks, pro fixes, and costs from $0 to $3,500+. Lennox Furnace — Won't ignite Lennox Furnace Won't Ignite: Causes, Fixes & Costs Lennox furnace won't ignite? Causes include a failed igniter, dirty flame sensor, closed gas valve and pressure switch faults — fixes and costs inside. Lennox Furnace — Blower not running Lennox Furnace Blower Not Running: Causes & Fixes Lennox furnace blower not running? Causes include a bad capacitor, blower motor, control board or door switch, plus fixes and US repair costs. Lennox Furnace — Blower won't shut off Lennox Furnace Blower Won't Shut Off: Causes & Fixes Lennox furnace blower runs constantly? Causes include thermostat fan settings, an open limit switch, or a stuck relay. DIY checks plus $0–$1,200 repair costs. Lennox Furnace — Clicking but not starting Lennox Furnace Clicking But Not Starting: Causes & Fixes Lennox furnace clicking but not starting? Causes include a stuck pressure switch, weak igniter, dirty flame sensor or open safety. Fixes and $0–$1,200 costs. Lennox Furnace — Flame sensor problems Lennox Furnace Flame Sensor Problems: Fixes & Costs Lennox furnace flame sensor problems cause dropouts and lockouts from a dirty or failed sensor. Cleaning runs $80-$180; replacement $150-$300.