Lennox Furnace error codes
34 Lennox furnace codes and problems, each with ranked causes, safe homeowner checks and honest repair costs. Count the flashes or read the code on your control board, then find it below. Legends vary by board revision, so confirm against the label inside your unit's door.
Of these, 33 need a professional repair and 1 is usually safe to check yourself.
| Code | What it means | Severity |
|---|---|---|
| Code E110 | Lennox Code E110 means low line voltage. Learn the causes, safe homeowner checks, technician diagnosis and repair costs from $0 DIY to $600+. | Call a pro |
| Code E111 | Lennox Code E111 means line voltage polarity is reversed. Causes, safe checks, technician fixes and honest US repair costs. | Call a pro |
| Code E112 | Lennox Furnace Code E112 means a ground fault or poor ground. Learn the causes, safe checks, technician diagnosis and repair costs. | Call a pro |
| Code E113 | Lennox Code E113 means high line voltage to the furnace. Causes, safe checks, technician diagnosis and repair costs for US homeowners. | Call a pro |
| Code E115 | Lennox Code E115 means low 24 VAC from an overloaded transformer or low-voltage wiring fault. Causes, safe checks, fixes and repair costs. | Call a pro |
| Code E125 | Lennox furnace Code E125 means the control board failed its internal self-check. Learn causes, safe checks and board replacement costs. | Call a pro |
| Code E131 | Lennox Code E131 means corrupted control parameters. Causes, safe checks, reconfiguration vs board replacement, and honest US repair costs. | Call a pro |
| Code E180 | Lennox Code E180 flags an outdoor air temp sensor fault (open, shorted, or out of range). Causes, safe checks, tech fixes and costs. | Call a pro |
| Code 200 (ignition lockout) | Lennox furnace showing code 200 ignition lockout with no heat? What it means, causes ranked, the flame-sensor fix, safe checks, and real repair costs. | Call a pro |
| Code E204 | Lennox Code E204 means a mis-wired gas valve. Learn the causes, safe checks, technician diagnosis, and honest US repair costs. | Call a pro |
| Code E205 | Lennox Furnace Code E205 means the gas valve relay is shorted or the valve is energized when it shouldn't be. Causes, fixes and repair costs. | Call a pro |
| Code E206 | Lennox Code E206 means a second-stage gas valve relay failure. Learn causes, safe checks, technician fixes and honest US repair costs. | Call a pro |
| Code E207 | Lennox Code E207 means a hot surface igniter open circuit. See causes, safe checks, technician diagnosis and honest US repair costs. | Call a pro |
| Code E208 | Lennox E208 means the low pressure switch failed to close. Causes, safe checks, tech diagnosis and repair costs from $0 DIY to $1,200. | Call a pro |
| Code E209 | Lennox Code E209 means the high-fire pressure switch failed to close. Causes, safe checks, tech diagnosis and repair costs from $0 DIY to $1,200 or more. | Call a pro |
| Code E210 | Lennox Code E210 is listed as a low-pressure switch failed closed. Causes, safe checks, technician diagnosis and repair costs from $0 DIY to about $1,200. | Call a pro |
| Code E211 | Lennox Code E211 is reported as high pressure switch failed closed. Verify the code number in your manual, then see causes, safe checks and repair costs. | Call a pro |
| Code E240 | Lennox Code E240 means low flame current in run mode from a dirty flame sensor or weak flame. Causes, fixes and honest US costs inside. | Call a pro |
| Code E241 | Lennox furnace Code E241 means flame is still present after the gas valve closes. Causes, safe checks, technician fixes and honest US repair costs. | Call a pro |
| Code E250 | Lennox Code E250 means the primary limit circuit is open from restricted airflow or overheating. Causes, safe checks, fixes and US repair costs. | Call a pro |
| Code E270 | Lennox furnace Code E270 means max ignition retries exceeded. Learn causes, safe checks, technician diagnosis and repair costs from $0 to $1,200. | Call a pro |
| Blower not running | Lennox furnace blower not running? Causes include a bad capacitor, blower motor, control board or door switch, plus fixes and US repair costs. | Call a pro |
| Blower won't shut off | 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. | DIY-friendly |
| Clicking but not starting | 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. | Call a pro |
| Flame sensor problems | Lennox furnace flame sensor problems cause dropouts and lockouts from a dirty or failed sensor. Cleaning runs $80-$180; replacement $150-$300. | Call a pro |
| Ignition lockout | Lennox furnace ignition lockout causes—igniter, flame sensor, gas supply, pressure switch—plus safe checks, tech diagnosis, and repair costs from $0 to $1,200. | Call a pro |
| Keeps shutting off | Lennox furnace keeps shutting off? Causes include dirty filters, flame sensor, limit and pressure switch faults — fixes and US repair costs. | Call a pro |
| Leaking water | Lennox furnace leaking water? Causes include clogged condensate drains, cracked traps and flue issues, plus fixes and honest US repair costs. | Call a pro |
| Loud bang on startup | A loud bang when your Lennox furnace ignites usually means delayed ignition or duct oil-canning. Safety steps first, then causes, checks, fixes and costs. | Call a pro |
| Pressure switch stuck open | Lennox furnace pressure switch stuck open: causes from blocked vents to a failing inducer, safe DIY checks, pro fixes, and real US repair costs. | Call a pro |
| 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+. | Call a pro |
| Short cycling | Lennox furnace short cycling? Common causes include dirty filters, overheating limits, flame sensor issues and oversizing—with fixes and US cost ranges. | Call a pro |
| Won't ignite | Lennox furnace won't ignite? Causes include a failed igniter, dirty flame sensor, closed gas valve and pressure switch faults — fixes and costs inside. | Call a pro |
| Won't turn on | Lennox furnace won't turn on? Common causes from thermostat and power to blown fuses and failed boards, with DIY checks and honest US repair costs. | Call a pro |
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