Lennox Gas Furnace Repair Manual

The Lennox Gas Furnace is a high-efficiency heating system designed for residential and light commercial applications. This manual covers installation, operation, maintenance, and troubleshooting procedures for various Lennox gas furnace models. Below are key sections for safety, features, installation, setup, operation, and troubleshooting.

Features at a Glance

Key components: Gas valve, heat exchanger, blower motor, ignition system, control board, pressure switches, and safety devices.

Installation Guidelines

Proper installation is critical for safe and efficient operation. Follow all local codes and manufacturer specifications.

1. Location: Install in well-ventilated area with adequate clearance for service access.
2. Venting: Properly size and install vent pipes according to furnace specifications.
3. Gas Connection: Use approved pipe and fittings; pressure test for leaks.
4. Electrical: Connect to proper voltage supply with appropriate circuit protection.
5. Ductwork: Ensure proper sizing and sealing for optimal airflow.

WARNING! Gas furnaces produce carbon monoxide. Proper venting is essential for safety. Only qualified technicians should perform installation.

Initial Setup and Startup

Follow these steps for proper furnace commissioning and initial operation.

1. Gas Pressure Check: Verify inlet and manifold gas pressures are within specifications.
2. Combustion Analysis: Check CO levels and combustion efficiency.
3. Airflow Verification: Measure static pressure and adjust blower speed if necessary.
4. Thermostat Setup: Program heating cycles and temperature settings.
5. Safety Check: Test all safety devices including limit switches and pressure switches.

CAUTION! Never bypass safety devices. Always verify proper operation before leaving the installation.

Technical Specifications

• Input Capacity: 40,000 to 120,000 BTU/H depending on model
• Efficiency: 80% to 98% AFUE
• Gas Type: Natural Gas or LP (conversion kit required)
• Electrical: 115V/60Hz, 15 amp circuit
• Static Pressure: 0.1 to 0.8 inches water column
• Venting: PVC, CPVC, or ABS for high-efficiency models
• Dimensions: Varies by model (check specific model documentation)
• Weight: 80 to 150 pounds depending on model

Controls and Settings

Access control board via front panel removal. LED status lights indicate system operation and error codes.

Control Board: POWER, STATUS LED, DIP switches, terminal strip for thermostat connection.

Temperature Settings: Adjust via thermostat. Blower Speed: Adjust dip switches or control board settings. Gas Pressure: Adjust at gas valve manifold. Limit Controls: Factory set - do not adjust. Pressure Switches: Verify proper operation during service.

System Components

Understanding furnace components is essential for proper diagnosis and repair.

1. Turn off power and gas supply before servicing any components.
2. Identify component locations: refer to unit-specific diagrams.
3. Test components according to manufacturer specifications.

Tip: Always verify component specifications before replacement.

Maintenance Procedures

Regular maintenance ensures optimal performance and extends equipment life.

1. Air Filter: Replace every 1-3 months depending on usage and environment.
2. Burner Cleaning: Inspect and clean burners annually.
3. Heat Exchanger: Visual inspection for cracks or damage.
4. Blower Assembly: Clean blower wheel and housing.
5. Drain System: Clear condensate lines and traps.
6. Ignition System: Check electrodes and flame sensor.
7. Venting: Inspect for obstructions or damage.
8. Safety Devices: Test all limit and pressure switches.

WARNING! Only qualified technicians should perform maintenance involving gas components or electrical systems.

Safety Features

Multiple safety systems protect against hazardous conditions. Flame Rollout Switches: Detect improper burner flames. High Limit Switches: Prevent overheating. Pressure Switches: Verify proper venting. Gas Valve: Shuts off gas supply during unsafe conditions.

Care & Cleaning

Regular cleaning maintains efficiency and prevents premature failure.

CAUTION! Always disconnect power before cleaning. Use approved cleaning solutions only. Never use water on electrical components.

Regulatory Information

UL certified for safety standards. ANSI Z21.47 compliant for gas appliance standards. Local codes may have additional requirements. Copyright © 2025 Lennox Industries Inc. All rights reserved. For technical support, contact Lennox at 1-800-9-LENNOX or visit www.lennox.com.

Troubleshooting Guide

Reset Procedure: Turn power off for 30 seconds, then restore power.

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