Introduction
When your Lennox flashes an error, you need clear next steps—fast. This GTA-ready guide decodes the most common E-codes with plain-English fixes and safety notes. If the code returns or mentions gas, rollout, or overheating, skip the guesswork and book furnace repair Toronto (yes, even with that typo—people search it) or standard furnace repair Greater Toronto with a licensed tech.
Read This First (Safety + Fast Wins)
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Smell gas, see soot/rollout, hear arcing? Power down and call a pro—now.
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Five quick checks before service:
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Replace the filter (correct size/MERV).
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Confirm power (furnace switch on, breaker not tripped).
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Open all vents and clear return grilles.
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Clear intake/exhaust (snow, lint, leaves).
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Reboot: thermostat OFF → cut power 60s → restore → HEAT. Note the code if it returns.
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Lennox Error Codes — Pro Triage (Code • Explanation • Solution)
| Code | Explanation | Solution |
|---|---|---|
| E 105 | System bus communication fault (controls/thermostat not “talking”). | Power-cycle, reseat low-voltage harness, inspect for damaged conductors; pro to test bus/board if it persists. |
| E 110 | Low line voltage detected. | Check breaker/shared circuits; verify voltage with a multimeter. Persistent low voltage: electrician/HVAC tech. |
| E 125 | Gas valve miswire/relay fault. | Don’t keep resetting. Verify wiring/polarity; tech to test coil/relay and replace if needed. |
| E 131 | Blower motor unresponsive (stuck wheel, seized bearings, failed ECM). | Kill power, clear obstructions, spin wheel by hand. If dead, tech to test ECM/windings and replace motor as required. |
| E 201 | Outdoor air temperature sensor failure (communicating systems). | Inspect connections; replace sensor if faulty. |
| E 223 | Low pressure switch open (draft/venting issue). | New filter; clear intake/exhaust; verify inducer and tubing. Tech to check switch set-point and vent lengths. |
| E240 | Limit switch circuit open (overheat). | Replace filter, open vents, verify blower speed/profile. Repeats: tech to measure temp rise/airflow and assess limit. |
| E270 | Flame not detected. | Clean/replace flame sensor; verify igniter and gas pressure. Tech to confirm flame current/ignition sequence. |
| E 275 | Flame detected out of sequence. | Inspect burner assembly for debris/misalignment; tech to test gas valve leakage and sensor wiring. |
| E290 | Indoor blower motor temperature too high. | New filter, clear returns/vents, clean blower wheel. Tech to check amps/bearings and airflow. |
| E 292 | Restricted airflow. | Replace filter first; inspect ducts for collapses/obstructions. Tech to measure static, adjust blower taps, add returns. |
| E 407 | Compressor start winding open (outdoor unit tie-in). | High-voltage diagnostics only—book a pro to test capacitor/windings and repair the outdoor unit. |
If a code returns immediately after the quick checks—or involves limit, rollout, gas valve, or motor overheat—book furnace repair Toronto right away.
Why these codes happen (and how pros fix them)
Airflow & Overheat (E 240, E 290, E 292)
Clogged filters, crushed flex, closed registers, or undersized returns push static pressure up and trip limits. Pros measure static pressure, verify temperature rise, right-size filter cabinets/returns, and set blower ramps for quiet, steady heat.
Ignition & Flame (E 270, E 275)
Weak/dirty flame sensors, aging igniters, or gas valve issues cause failed or out-of-sequence ignition. Techs check flame current (µA), burner alignment, and manifold pressure; they clean burners and replace worn parts.
Venting/Draft & Pressure Switches (E 223)
Blocked intake/exhaust, condensate in pressure tubing, or inducer faults open the switch. Expect a termination check, tubing purge, inducer test, and vent pitch/length corrections.
Power & Controls (E 105, E 110, E 201, E 125)
Loose low-voltage wiring, brownouts, failed sensors, or miswired valves trigger these. Pros validate line voltage, inspect harnesses, update firmware where applicable, and replace sensors/boards.
Outdoor Unit Tie-ins (E 407)
Communicating systems can surface outdoor faults on the furnace controller—strictly pro territory due to high voltage and refrigerant.
DIY That’s Safe (and actually useful)
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Filters: set reminders; keep spares for winter.
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Returns: vacuum grilles; don’t block with furniture/boxes.
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Condensate: eyeball traps/hoses for kinks or algae during filter changes.
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Thermostat: ensure staging/fan profiles match your furnace after any thermostat swap.
When to stop troubleshooting
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Gas/rollout/limit codes or repeated lockouts
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Electrical smells, tripping breakers, melted insulation
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Not comfortable using a multimeter or accessing the blower
At that point, book professional furnace repair Toronto (and yes, searches for furnace repair GTA will find us too). We diagnose, repair, and reset safely—with clear pricing and same-day options across the GTA.
Service Area & Quick Links
FAQ: Lennox Furnace Error Codes (Toronto Homeowner Guide)
Q1. What does Lennox Error Code E 105 mean?
E 105 signals a device communication problem on the RS-Bus — the furnace control isn’t “talking” to other devices (e.g., thermostat). Reseat low-voltage wiring at the board/thermostat and check for damaged harnesses. If it returns, book a pro to test the control bus and board.
Q2. What is Error Code E 110 (low line voltage)?
E 110 means the unit detected low supply voltage. Check the breaker and shared circuits; if you have a multimeter, confirm stable voltage. Persistent low voltage needs an electrician or HVAC technician.
Q3. What does Error Code E 201 indicate?
E 201 usually means the outdoor air temperature sensor failed or is unplugged. Inspect wiring; replacing the sensor typically resolves it. Call a certified tech if you’re unsure.
Q4. What is Error Code E 223 and is it dangerous?
E 223 indicates a hard lockout related to the rollout circuit opening (or having been open). Shut the system off. Possible causes include a blocked vent, improper gas pressure, or burner flame rollout. Have a licensed technician inspect the rollout switch, burners, and venting.
Q5. What causes Error Code E 292 (restricted airflow)?
E 292 points to restricted airflow — most often a dirty filter, blocked return/supply, collapsed flex, or blower issues. Replace the filter first; if airflow’s still weak, have a pro check ducts and blower alignment.
Q6. What does Error Code E 240 (limit switch open) mean?
E 240 means the limit circuit is open, usually from overheating due to poor airflow. Install a clean filter, open all vents, and ensure returns aren’t blocked. If it repeats, a technician should verify temperature rise, blower settings, and the limit switch.
Q7. What is Error Code E 407 (compressor start winding open)?
E 407 indicates the compressor’s start winding circuit is open (on systems paired with AC/heat pump). This is high-voltage work — book an HVAC professional to test the capacitor/windings and repair safely.
Need help now?
If your Lennox keeps throwing codes—especially E 240, E 270, E 275, E 292—don’t keep resetting. Book furnace repair Toronto with For Saving Home Services Inc for diagnostics, clean repairs, and reliable heat tonight.
