Lennox Gas Furnace Repair

Need help with your Lennox gas furnace? This guide covers common problems and fixes.

Many furnace issues can be solved without calling a professional. But always put safety first with gas appliances.

Know Your Lennox Furnace

Lennox makes different furnace models. Some are basic. Others are high-efficiency systems. All work similarly though. They burn gas to heat air. A blower sends this warm air through ducts to heat your home.

Find your model number before doing anything else. Look inside the front panel or on the rating plate. Write it down somewhere safe.

The G40 series often has ignition problems as they get older. ML180 models typically have pressure switch issues when they act up. The EL195 series sometimes has flame sensor problems that cause shutdowns.

Gas Furnace Safety

• Never skip safety steps with gas furnaces.

• Turn off the power first. Find the switch on the furnace or flip the right breaker in your electrical panel.

• Shut off the gas supply valve too. It's usually near the furnace. Turn the handle so it runs across the pipe instead of along it.

• Don't mess with gas valves or gas lines. Leave that to the furnace repair pros. Too risky.

• Wait till the furnace cools if it's been on recently. Metal parts stay hot for a while.

• Keep carbon monoxide detectors in your home. Test them regularly. Carbon monoxide has no smell but can kill.

• Smell gas? Stop everything. Don't touch switches or make sparks. Get out and call the gas company from outside your home.

What Goes Wrong With Lennox Furnaces

Furnaces show clear signs when they have problems.

• No heat might mean no power, no gas, or thermostat issues.

• Starts then shuts off quickly? Probably a safety switch doing its job. Often caused by dirty filters or flame sensor problems.

• Running but not much heat coming out suggests airflow problems, blower issues, or gas pressure problems.

• Weird noises mean different things. Scraping sounds? Check the blower wheel. Rumbling might be delayed ignition. High squealing usually means motor bearings are going bad.

• Blower won't stop running? Could be a control board problem or stuck relay.

• Cold spots in rooms often point to airflow or duct problems.

• High gas bills without more usage mean the furnace isn't working efficiently anymore.

Check Thermostat and Power First

Start with the simple stuff before tearing into your furnace.

• Make sure the thermostat works and has power. Dead batteries cause needless service calls. Check that it's set to "heat" and the temperature is higher than the room.

• Look at your circuit breakers. Reset any tripped ones.

• Check the furnace power switch. Looks like a light switch on the unit or wall nearby. Gets turned off accidentally sometimes.

• Make sure all access panels are closed tightly. Door safety switches prevent operation when panels are loose.

• Look for blown fuses on the control board. Replace any bad ones with exactly the same type.

Air Filter and Airflow Issues

Dirty filters cause tons of furnace problems. Fix this first.

• Find your filter. It usually slides in near the blower or return duct. Some homes have filters at the return grills instead.

• If you can't see light through it when held up, replace it. Use the right size and type.

• Furnaces need good airflow or they overheat. When they overheat, safety switches shut them down.

• Check that supply and return vents aren't blocked by furniture or rugs. Closing too many vents creates back pressure that damages the furnace.

• Stuffy air when the furnace runs suggests poor return air. This makes the furnace work too hard.

The G61 Lennox models hate airflow restrictions. Even slightly dirty filters make them shut down.

Fixing Ignition Problems

Modern furnaces use electronic ignition systems that can act up.

• Clicking sounds without ignition mean the system's trying but failing to light the gas.

• Hot surface igniters glow to light gas. They burn out eventually. Don't touch them with bare hands - oils from skin damage them.

• Flame sensors get carbon buildup over time. This makes them shut off the gas soon after lighting. Clean them with fine sandpaper or steel wool. Just rub the metal rod gently.

• Spark igniters on older models create a spark to light gas. They wear out or get knocked out of position. The spark gap must be exactly right.

• High-efficiency models often use combination spark igniter/flame sensor units. These need precise positioning. Even small movements cause problems.

Make sure gas supply is adequate too. Low gas pressure causes weak flames and poor operation.

Blower Motor Problems

The blower moves air through your system. When it fails, you get no heat distribution.

• Listen for odd noises. Squealing or grinding usually means bearings are failing. Fix this quickly before the motor seizes.

• Check if the blower wheel turns easily when power is off. If it's hard to turn or scrapes, something's interfering with it. The wheel sometimes comes loose or gets debris stuck in it.

• Newer Lennox furnaces use ECM variable-speed motors. These have electronic control modules attached. When the modules fail, you often need the whole motor assembly.

• The blower might run at wrong speeds. Happens when speed control switches get damaged or the control board acts up. Elite series furnaces sometimes do this after power outages.

• Motors overheat and shut down if covered in dust. The dust acts like a blanket, trapping heat.

• Start capacitors help motors get going. Bad ones make motors hum without starting. Look for swelling or bulging tops on capacitors.

Pressure Switch Problems

Pressure switches are safety devices that ensure proper venting. They often cause furnace shutdowns.

• They won't close if there's poor draft. Check exhaust and intake pipes for blockages. Leaves, bugs, or ice can trigger these switches.

• Look at the small tubes connecting switches to the furnace. Cracked or disconnected tubes prevent proper pressure readings.

• Water in the exhaust system happens in high-efficiency models. This can block flow and trigger pressure switches.

• The inducer motor creates draft needed to close pressure switches. If it runs weakly or not at all, switches stay open. Listen for it before ignition.

ML180V models often have pressure switch issues after a few years. The switches themselves sometimes fail.

Never bypass these switches. They protect against carbon monoxide poisoning. If they're shutting down your furnace, there's a reason.

Reading Control Board Signals

The control board runs everything in your furnace. It monitors all safety systems.

Most Lennox furnaces have diagnostic lights on the board. They blink in patterns to tell you what's wrong. Check the panel inside your furnace or your manual to decode them.

• 3 flashes often means pressure switch problems

• 4 flashes typically means a limit switch is open

• 5 flashes often indicates flame sensing issues

• 7 flashes usually means gas valve problems

Boards themselves fail sometimes. Signs include completely dead furnace, random operation, or blower running when it shouldn't.

Look for burn marks on the board. These mean electrical problems that usually require replacement.

Check for loose connections. Push each wire connector gently to make sure it's tight.

Some boards have resettable circuit breakers. Look for small buttons that may have popped out.

Keep Your Furnace Running Right

• Change filters regularly. Every 1-3 months depending on your home. Pet owners need more frequent changes.

• Keep the furnace area clean and clear. No stored items nearby. Furnaces need air circulation.

• Check outside exhaust and intake pipes each fall. Clear any blockages. Make sure they're in good shape.

• Pay attention to furnace sounds. New noises almost always mean problems starting. Fix them early.

• Clean the blower assembly yearly. Dust buildup hurts efficiency and causes overheating.

• Have professional furnace HVAC maintenance and inspection before the heating season starts. Small adjustments keep things running safely.

• Clean dust from the burner area once a year. Buildup affects flame patterns and efficiency.

Test carbon monoxide detectors monthly. Replace the batteries yearly. This protects your family if something goes wrong.

Getting Replacement Parts

Need parts for your Lennox furnace? Sears Parts Direct has genuine replacement components. Use your model number to get the right parts.

Don't use generic parts for important components like control boards or gas valves. Small differences matter for performance and safety.

Some parts look alike but have different specs. Match electrical ratings and part numbers exactly.

Keep old parts until the repair works well. Sometimes you need to compare them or return defective replacements.

Control boards must match your model precisely. Even slight variations cause compatibility problems.

When to Get Help

Some repairs need professional furnace repair service:

• Gas valve or gas line issues always need certified technicians. The safety risk of repairing gas components yourself is too high.

• Heat exchanger problems require professional work. Cracked exchangers can leak carbon monoxide.

• Complex electrical issues beyond basic testing need special equipment.

• Multiple failed components need professional diagnosis to find the root cause.

• Internal control problems shown by diagnostic codes often need professional help.

If your Lennox furnace needs repairs you're not comfortable tackling, give us a call. Our appliance repair team knows these systems well and can fix them right the first time.