Lennox G20 Series Gas Furnace

General Safety Warnings

⚠️ WARNING: If the information in this manual is not followed exactly, a fire or explosion may result causing property damage, personal injury, or death.

• Do not store or use gasoline or other flammable vapors and liquids in the vicinity of this or any other appliance.
• Installation and service must be performed by a qualified installer, service agency, or the gas supplier.

Immediate Actions in Case of Gas Leak:

• Do not try to light any appliance.
• Extinguish any open flames.
• Do not touch any electrical switch; do not use any phone in your building.
• Immediately call your gas supplier from a neighbor's phone. Follow the gas supplier's instructions.
• If you cannot reach your gas supplier, call the fire department.

This product is certified by the American Gas Association and approved by the Canadian Standards Association.

Parts Identification

Diagram 1: Lennox G20E / G20X Parts Identification

Figure 1 shows an exploded view of the Lennox G20E/G20X furnace, illustrating its main components. These include the Cabinet Cap, Upper Access Panel, Gas Manifold, Gas Valve, Burner Box Damper Assembly, Top Strip, Draft Hood, Ignition Control, Roll-out Switch, Pilot/Electrode Assembly, Burners, Removable Burner Box Top, Burner Box, Limit Control, Blower, Control Box, Rear Baffle, Heat Exchanger, and Cabinet.

Important Safety Information and Warnings

Important Directions for Safe Operation

1. Keep the furnace area clear and free of combustible material, gasoline, and other flammable vapors and liquids. If installed in an insulated area, furnace must be kept free of insulating material, as it may be combustible.
2. Inspect the furnace venting system to ensure it is in place, physically sound, and without holes, corrosion, or blockage.
3. Inspect the furnace return air duct connection to ensure it is sealed to the furnace and terminates outside the space containing the furnace.
4. Inspect the physical support of the furnace to guarantee it is sound without sagging, cracks, or gaps around the base, and maintains a seal between the base and support.
5. DO NOT obstruct airflow to the unit. The unit must receive an unobstructed flow of combustion and ventilating air.
6. DO NOT store chlorine or fluorine products near the unit or introduce them into the combustion air, as these products can cause furnace corrosion.
7. DO NOT draw return air from a room where this furnace or any other gas appliance (e.g., a water heater) is installed. Drawing return air from such a room creates negative pressure, which can cause flue products to be pulled back down the vent pipe and into the room, potentially leading to incomplete combustion and carbon monoxide gas formation.

Your furnace is a gas appliance. Complete combustion of the gas is critical to avoid the production of carbon monoxide gas. This requires correct gas pressure and flow rate, adequate combustion air, and proper venting.

Your furnace is designed to meet national standards and operate safely when properly installed and maintained. However, performance can be impacted by installation and operating environment. It is your responsibility to ensure the appliance is maintained. Proper maintenance is critical for your safety and satisfactory operation.

Lennox strongly recommends annual inspection and maintenance. Contact your independent Lennox dealer for an inspection by a qualified service technician.

Lighting Information and Operation

Before Operating: Smell all around the appliance area for gas, especially near the floor, as gas is heavier than air and settles low. Use only your hand to push in or turn the gas control knob or lever. Never use tools. If the knob or lever will not push in or turn by hand, do not try to repair it; call a qualified service technician. Force or attempted repair may result in a fire or explosion.

To Place G20E or G20X Furnace into Operation:

G20E or G20X units are equipped with an intermittent pilot ignition system. Do not attempt to manually light pilots on these furnaces. Each time the thermostat calls for heat, the pilot will automatically light. The pilot does not burn when there is no call for heat on units with electronic ignitions.

Gas Valve Operation (Diagrams 3 and 4)

1. STOP! Read the safety information at the beginning of this section.
2. Set thermostat to lowest setting. (See Diagram 2).

Diagram 2: Thermostats

Illustrates a typical thermostat with controls for Heat/Cool, Fan (Auto/On), and temperature settings.

3. Turn off all electrical power to the appliance.
4. This appliance is equipped with an ignition device which automatically lights the pilot. Do not try to light the pilot by hand.
5. Remove control access panel.
6. Honeywell VR8204 Gas Valve: Turn the knob on the gas valve clockwise to OFF. (See Diagram 3).
7. Robertshaw 7200 Gas Valve: Depress the lever and move to OFF position. Do not force. (See Diagram 4).

Diagram 3: Honeywell VR8204 Series Gas Valve

Shows the gas valve with ON and OFF positions, with the valve illustrated in the OFF position.

Diagram 4: Robertshaw 7200 Gas Valve

Shows the gas valve selector arm in the OFF position.

7. Wait five (5) minutes to clear out any gas. If you then smell gas, STOP! Immediately call your gas supplier from a neighbor's phone. Follow the gas supplier's instructions. If you do not smell gas, go to the next step.
8. Honeywell VR8204 Gas Valves: Turn the knob on the gas valve counterclockwise to ON.
9. Robertshaw 7200 Gas Valve: Depress the lever and move to ON position. Do not force.
10. Replace control access panel.
11. Turn on all electrical power to the unit.
12. Set thermostat to desired setting.

NOTE: When the unit is initially started, steps 1 through 11 may need to be repeated to purge air from the pilot line.

If the furnace still will not operate, follow the instructions "To Turn Off Gas To Unit" and call your service technician or gas supplier.

To Turn Off Gas To Unit

1. Set thermostat to lowest setting.
2. Turn off all electrical power to unit if service is to be performed.
3. Remove control access panel.
4. Honeywell VR8204 Gas Valves: Turn the knob on the gas valve clockwise to OFF.
5. Robertshaw 7200 Gas Valve: Depress the lever and move to OFF position. Do not force.
6. Replace control access panel.

Maintenance and Inspection

Filters

G20E and G20X series units are equipped with reusable filters that should be inspected monthly and cleaned when necessary for proper furnace operation. Refer to Table 1 for filter sizes.

Filter Cleaning Procedure:

1. Turn off electric power to the furnace.
2. Remove blower access panel. Wait for the blower to stop.
3. Remove filter by sliding it up and out of its brackets.
4. Wash filter with water and a mild detergent. For increased efficiency, the filter media can be sprayed with filter Handicoater when dry (RP Products no. 418, Lennox part no. P-8-5069).

NOTE: If filter media must be replaced, order Lennox part no. P-9-7831 for 20” x 25” filter, P-8-7822 for 16" x 25" filter, 97H0601 for 18" x 25" filter, 97H0701 for 25" x25" filter, and 97H0801 for 24” x 30” filter.

5. Reinstall filter. Slide filter into the top bracket and drop into the lower bracket.

NOTE: Do not replace reusable foam filters with throw-away filters.

6. Replace blower access panel.

Table 1: Filter Sizes

Blower

Check and clean the blower wheel for any debris. The blower motor is prelubricated for extended bearing life; no further lubrication is needed.

Pilot and Burner Flame

1. Pilot Flame (Diagram 7): The pilot flame must surround the end of the flame sensor for proper operation of the pilot safety circuit.

Diagram 7: Pilot Flame (Side View)

Shows the pilot assembly including the Pilot Gas Line, Flame Sensor, and Electrode (G20E & G20X).

2. Burner Flame (Diagram 8): Start the burner and allow it to operate for a few minutes to establish normal burning conditions. Check the burner flame by observation. The flame should be predominantly blue in color, strong in appearance, and rise directly from the burner ports in the heat exchanger. Ensure the flame is burning from all continuous ribbon ports and does not impinge on the sides of the heat exchanger.

Diagram 8: Burner Flame

Illustrates the burner flame. The note indicates viewing the burner flame through an observation port on the burner box or damper opening (not shown).

Venting System Inspection

Annually (before the heating season), inspect the furnace venting system, draft hood, vent cap, heat exchanger, burners, and pilot for corrosion, deterioration, or deposits of debris. Remove any obstructions.

Contact your Lennox dealer for a periodic unit inspection by a qualified service technician.

Blocked Vent Shut-off System

Your Lennox furnace is equipped with a blocked vent shut-off switch and a flame roll-out switch. The blocked vent shut-off switch shuts off the gas supply to the furnace in the event of flue or vent blockage. The flame roll-out switch shuts off the gas supply to the furnace if there is a blockage of the heat exchanger. If the furnace fails to operate due to the functioning of either of these switches, DO NOT attempt to place the furnace into operation. Contact a qualified service person.

Service Reminders and Safety Precautions

Service Reminder

Call your Lennox service technician if the unit is inoperative. Before calling, always check the following to be sure service is required:

1. Check to see that electrical disconnect switches are ON.
2. Check room thermostat for proper setting.
3. Replace any blown fuses or reset circuit breakers.
4. Gas valve should be ON.
5. Air filter should not be plugged, limiting airflow.
6. Is gas turned on at the meter?
7. Is the manual main shut-off valve open?

Safety Precautions

To keep your Lennox gas heating system in peak operating condition year after year, contact your independent Lennox dealer about a planned service program.

If you discover any of the following, shut down your unit and contact an independent Lennox dealer for an inspection by a qualified technician:

• If you repeatedly hear any new or unfamiliar sounds while your unit is operating, there may be a problem. For example, poorly performing burners can produce unfamiliar noises.
• If you smell any unusual odors, your unit may be operating improperly. For example, units can give off unfamiliar odors if components are required to operate in abnormal conditions.
• Look for visible signs of a malfunctioning unit. Examples include unusual amounts of condensate on windows inside your house, visibly burnt components, or unusual dirt or rust accumulations on the vent pipe or in the unit.
• If you experience headache, nausea, fatigue, or dizziness, the cause could be exposure to carbon monoxide gas. This is often misdiagnosed as the flu because symptoms are similar. If you suffer from flu-like symptoms that are exaggerated at home but seem to subside while you are away from the house, exposure to carbon monoxide could be the cause.

Your vigilance may pay off in early detection of a problem before either personal injury or property damage occurs. Do not hesitate to contact a qualified service technician as an investment in your well-being.

Planned Service

You should expect a service technician to check the following items during an annual inspection. Power to the unit must be shut off for the service technician's safety.

• Fresh air grilles and louvers (on the unit and in the room where the furnace is installed) - Must be open and unobstructed to provide combustion air.
• Burners - Must be inspected for rust, dirt, or signs of water.
• Vent pipe - Must be inspected for signs of water, damaged or sagging pipe, or disconnected joints.
• Unit appearance - Must be inspected for rust, dirt, signs of water, burnt or damaged wires, or components.
• Blower access door - Must be properly in place and provide a seal between the return air and the room where the furnace is installed.
• Return air duct - Must be properly attached and provide an air seal to the unit.
• Operating performance - Unit must be observed during operation to monitor proper performance of the unit and the vent system.
• Combustion gases - Flue products must be analyzed and compared to the unit specifications.

Problems detected during the inspection may make it necessary to temporarily shut down the furnace until the items can be repaired or replaced.

Pay attention to your furnace. Situations can arise between annual furnace inspections that may result in unsafe operation. For instance, items innocently stored next to the furnace may obstruct the combustion air supply. This could cause incomplete combustion and the production of carbon monoxide gas.