Goodman GMS8 Furnace Manual

The Goodman GMS8 is a high-efficiency gas furnace with AFUE ratings up to 80%, single-stage operation, durable heat exchanger, multi-speed blower motor, direct spark ignition, pressure switch safety, thermal overload protection, and compatibility with standard thermostat systems. Designed for residential heating applications with input capacities ranging from 40,000 to 120,000 BTU/h. Below are key sections for safety, features, installation, setup, operation, and troubleshooting.

1. Features at a Glance 2. Installation 3. First-Time Setup 4. Specifications 5. Controls and Settings 6. Connecting Components 7. Operating Procedures 8. Safety Features 9. Maintenance & Cleaning 10. Regulatory Information 11. Troubleshooting

Features at a Glance

Key components: Durable aluminized steel heat exchanger, direct spark ignition system, multi-speed blower motor, pressure switch, flame sensor, gas valve, and integrated control board.

Feature	Description
Heat Exchanger	Aluminized steel construction for durability and efficiency
Ignition System	Direct spark ignition for reliable startup
Blower Motor	Multi-speed ECM motor for optimized airflow
Pressure Switch	Ensures proper venting before ignition
Flame Sensor	Monitors burner flame for safety shutdown
Gas Valve	Regulates gas flow to burner assembly
Control Board	Integrated microprocessor for system operation
Thermal Overload	Protects motor from overheating
Limit Switch	Prevents overheating of heat exchanger
Drain Connection	For condensate removal in high-efficiency models

Installation

Unpack and inspect all components. Ensure proper clearances and venting requirements.

Position furnace: Place on stable, level surface with proper clearances (minimum 1 inch from combustible materials).
Connect gas supply: Use approved gas piping with sediment trap; pressure test for leaks.
Install venting: Use approved PVC or metal vent pipe per local codes.
Electrical connections: Connect 120V power supply and thermostat wiring.
Drain line: Install condensate drain line with proper slope.

WARNING! Gas furnaces must be installed by qualified technicians only. Follow all local codes and manufacturer specifications.

First-Time Setup

Complete installation verification and initial startup procedure.

Gas pressure adjustment: Set manifold pressure to specifications on rating plate.
Blower speed setting: Adjust blower speeds for heating mode as required.
Thermostat configuration: Connect compatible thermostat and set heating mode.
System check: Verify proper ignition sequence and flame operation.
Airflow measurement: Check static pressure and temperature rise.

CAUTION! Never bypass safety controls. Ensure proper combustion air and venting before operation.

Specifications

Model Series: GMS8
AFUE Rating: Up to 80%
Input Capacity: 40,000 - 120,000 BTU/h
Gas Type: Natural Gas
Stages: Single-stage operation
Blower Type: Multi-speed direct drive
Ignition: Direct spark
Voltage: 120V AC, 60Hz
Sound Rating: Standard residential levels
Warranty: Limited lifetime heat exchanger, 10-year parts

Controls and Settings

Access control board via front panel. Integrated LED diagnostic light for error codes.

Thermostat Connections: R (24V power), W (Heat), G (Fan), C (Common)

Blower Speeds: Adjustable heating speed via motor taps. Gas Pressure: Factory set, adjustable if needed. Limit Settings: Fixed temperature limits. Diagnostic Codes: Flash patterns indicate specific faults (1 flash = pressure switch, 2 flashes = ignition failure, etc.).

Connecting Components

Gas supply: 1/2" to 3/4" black iron pipe. Electrical: 120V power, 24V thermostat. Venting: 2" to 3" PVC or metal.

Turn off gas and electrical power before making connections.
Use pipe compound on gas threads; pressure test to 14" WC.
Follow wiring diagram for proper thermostat connections.
Ensure vent pipes slope upward away from furnace.

Tip: Always use two wrenches when connecting gas piping to prevent damage to valves.

Operating Procedures

Standard heating cycle operation and normal sequence of operations.

Call for heat: Thermostat closes W to R circuit.
Inducer operation: Pressure switch proves venting.
Ignition sequence: Hot surface igniter glows, gas valve opens.
Flame proving: Flame sensor confirms ignition.
Blower activation: Blower starts after heat exchanger warm-up delay.
Cycle completion: Thermostat satisfied, gas valve closes, blower runs for post-purge.

WARNING! Never operate furnace without proper venting and combustion air. Monitor for unusual noises or odors.

Safety Features

Pressure switch: Prevents operation if venting blocked. Flame rollout switch: Detects burner compartment overheating. Limit switch: Protects against heat exchanger overheating. Flame sensor: Ensures gas valve closes if no flame detected.

Maintenance & Cleaning

Annual professional maintenance recommended. Replace air filter monthly during heating season.

CAUTION! Turn off gas and electrical power before servicing. Use only manufacturer-approved replacement parts.

Regulatory Information

ANSI Z21.47: Certified for natural gas operation. UL listed. Complies with U.S. Department of Energy efficiency standards. Copyright © Goodman Manufacturing Company, L.P. For technical support, visit www.goodmanmfg.com or contact 1-877-466-8626.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No heat	Thermostat/Power	Check thermostat setting; verify 120V power; check door switch.
Furnace won't start	Safety lockout	Reset power; check diagnostic LED; verify pressure switch operation.
Short cycling	Airflow/Filter	Replace dirty filter; check for blocked vents; verify blower operation.
Blower runs continuously	Thermostat setting	Check fan setting (Auto/On); verify thermostat wiring.
Gas odor	Leak/Incomplete combustion	Immediately shut off gas; evacuate area; call professional service.

Reset: Turn power off for 30 seconds then restore.

Service: 1-877-466-8626; www.goodmanmfg.com