Lennox Furnace Troubleshooting Manual

The Lennox Furnace is a high-efficiency heating system designed for residential use, featuring advanced diagnostics, variable-speed blower technology, and multiple safety systems. This troubleshooting manual covers common issues, diagnostic procedures, safety precautions, and maintenance guidelines for Lennox furnace models. Below are key sections for safety warnings, common problems, diagnostic codes, maintenance procedures, and technical specifications.

1. Safety Precautions 2. Common Issues & Solutions 3. Diagnostic Error Codes 4. Maintenance Procedures 5. Technical Specifications 6. Component Identification 7. Reset Procedures 8. Professional Service 9. Warranty Information 10. Regulatory Compliance 11. Frequently Asked Questions

Safety Precautions

Before attempting any troubleshooting, ensure proper safety measures are followed to prevent injury or equipment damage.

Safety Measure	Description
Power Disconnect	Turn off electrical power at circuit breaker before servicing
Gas Valve Shutoff	Close gas supply valve before working on gas components
Carbon Monoxide Detection	Install CO detectors near furnace and sleeping areas
Clearance Requirements	Maintain minimum clearances from combustible materials
Ventilation	Ensure proper airflow and venting for combustion
Professional Assistance	Contact qualified technician for complex repairs
Hot Surface Warning	Allow furnace to cool before touching internal components
Electrical Grounding	Ensure proper grounding of all electrical components

Common Issues & Solutions

Most common furnace problems and their basic troubleshooting solutions.

Furnace won't start: Check thermostat settings, circuit breaker, and gas supply.
No heat production: Verify pilot light (if applicable), gas valve position, and air filter condition.
Insufficient heating: Replace dirty air filter, check ductwork for obstructions.
Frequent cycling: Clean flame sensor, check thermostat location and calibration.
Unusual noises: Inspect blower wheel, motor bearings, and heat exchanger for issues.

WARNING! Gas appliances can be dangerous if improperly serviced. Always shut off gas and electricity before inspection.

Diagnostic Error Codes

Lennox furnaces display error codes to help identify specific problems.

Check status light: Observe blinking pattern on control board.
Code interpretation: Refer to manufacturer's code chart for specific meanings.
Common codes: E200 (pressure switch), E300 (ignition failure), E400 (limit switch).
Reset procedure: Power cycle furnace after addressing error condition.

CAUTION! Repeated error codes indicate persistent problems requiring professional service.

Maintenance Procedures

Monthly: Check air filter, clean if reusable or replace if disposable.
Seasonal: Inspect vent pipes, clean flame sensor, verify safety controls.
Annual: Professional inspection of heat exchanger, burners, and electrical components.
Filter Replacement: Use manufacturer-recommended filters for optimal performance.
Blower Maintenance: Clean blower assembly and check belt tension (if applicable).
Duct Inspection: Check for leaks and proper insulation in ductwork.
Thermostat Calibration: Verify accurate temperature readings and proper operation.

Technical Specifications

Access control panel via front cover removal. Main Components: Control board, gas valve, ignitor, flame sensor, blower motor, limit switches.

Controls: Power switch, thermostat connections, diagnostic LED, reset buttons.

Heating: BTU output range, AFUE rating, temperature rise specifications. Electrical: Voltage requirements, amp draw, circuit protection. Gas: Input BTU, manifold pressure, orifice sizes. Airflow: CFM ratings, static pressure limits, filter specifications.

Component Identification

Gas Valve: Controls gas flow to burners. Ignitor: Electronic or hot surface ignition. Flame Sensor: Detects burner flame. Pressure Switches: Verify proper venting. Limit Switches: Prevent overheating.

Locate control board for diagnostic information.
Identify gas train components for leak testing.
Find safety switches for system verification.

Tip: Refer to unit-specific wiring diagram for component locations.

Reset Procedures

Various reset methods for different furnace conditions.

Power reset: Turn off circuit breaker for 30 seconds, then restore power.
Control board reset: Press reset button if equipped (consult model manual).
Lockout reset: Address underlying issue first, then power cycle unit.
Thermostat reset: Remove batteries or power down for system reboot.
Manual reset switches: Locate and press high-limit reset buttons.
Error code clear: Correct problem causing error code display.
Factory reset: Use only when directed by technical support.

WARNING! Do not repeatedly reset without addressing root cause of problems.

Professional Service

When to contact a qualified Lennox technician for service.

Warranty Information

CAUTION! Unauthorized repairs may void manufacturer warranty.

Regulatory Compliance

UL certified for safety standards. ANSI Z21.47 compliant for gas appliances. Meets DOE efficiency requirements. For technical support, visit www.lennox.com or contact 1-800-9-LENNOX. Installation must comply with local building codes and NFPA standards.

Frequently Asked Questions

Question	Common Cause	Solution
Furnace blows cold air	Ignition failure	Check gas supply, clean flame sensor, verify ignitor operation.
Unit cycles on/off frequently	Dirty filter/overheating	Replace air filter, check airflow restrictions, clean heat exchanger.
Strange burning smell	Dust accumulation	Normal during first seasonal use; persistent smells require inspection.
High utility bills	Efficiency issues	Check filter, duct leaks, thermostat settings, and system maintenance.
Pilot light won't stay lit	Thermocouple issues	Clean or replace thermocouple, check gas pressure and draft.

Emergency: Smell gas? Evacuate immediately and call gas company from outside.

Service: 1-800-9-LENNOX; www.lennox.com