Furnace Repair: Problems, Safe Checks and Local Help

A furnace tends to fail on the coldest night of the year, which is exactly when a homeowner starts searching for furnace repair. This page explains what the common symptoms usually mean, which checks you can do safely before anyone arrives, the situations where you should stop and get out of the house, and how to reach an independent local heating contractor through LocalRepairLine. LocalRepairLine is a referral service, not a contractor, and this is general information rather than a substitute for an in-person inspection.

Furnace not heating your home? Call and describe what is happening and LocalRepairLine will connect you with an independent heating contractor who serves your area and nearby towns. We are a referral service, not a contractor.

Common furnace problems and what they usually mean

Furnaces fail in predictable ways, and the symptom usually narrows the cause to a short list. Use the sections below to work out whether a simple check might get the heat back or whether the furnace needs a professional.

Furnace won't turn on at all

Nothing happens when the thermostat calls for heat. Start with the obvious: thermostat batteries, the thermostat mode set to heat, the furnace power switch (it looks like a light switch on or near the furnace), the breaker, and the furnace door. Most furnaces have a door safety switch that cuts power if the blower panel isn't seated. If all of those check out, the control board, transformer or a safety switch has likely opened, and that's a job for a technician. Our furnace not heating checklist walks through these in order.

Furnace runs but blows cold or lukewarm air

If the blower runs but the air is cool, the burners aren't lighting or are shutting down early. Common causes are a dirty flame sensor, a failed igniter, a clogged filter overheating the furnace and tripping the limit switch, or a thermostat fan setting left on ON instead of AUTO (which runs the blower between heating cycles and feels like cold air). Our furnace blowing cold air guide covers each cause and which ones you can check yourself.

Furnace starts, runs a few minutes, then shuts off (short cycling)

Short cycling is most often a dirty flame sensor that can't confirm the flame, a clogged filter or closed vents overheating the heat exchanger, or a blocked intake or exhaust pipe on a high-efficiency furnace. Less often it's an oversized furnace or a failing control board. Replace the filter and open all supply vents first; if it keeps cycling, a technician can test the flame sensor, limit switch and pressure switch.

Igniter clicks but the burners never light

Repeated clicking with no flame on a spark-ignition furnace, or a glow with no flame on a hot-surface igniter, points to the gas valve not opening, a closed gas shutoff, low gas pressure, or a dirty burner. Confirm the gas shutoff on the pipe to the furnace is open (handle parallel to the pipe) and that other gas appliances work. Beyond that, don't attempt to work on the gas train; call a professional.

Loud bang, rattle, squeal or grinding

A bang at startup often means delayed ignition: gas builds up for a moment before it lights, which is a burner or igniter problem that should be looked at. A metallic rattle is usually a loose panel or duct. A high squeal points to a blower belt or motor bearing, and grinding means the blower motor is failing. Turn the furnace off at the switch if you hear grinding; running a seized motor can damage the control board.

Furnace runs nonstop and the house is still cold

A furnace that never satisfies the thermostat may have a badly clogged filter, closed or blocked vents, leaking ductwork, a failed lower-stage burner on a two-stage unit, or a thermostat that's mislocated or miswired. On very cold days a correctly sized furnace will run long cycles, so compare the symptom with how the house felt last winter.

Pilot light or hot-surface igniter keeps failing

On older furnaces with a standing pilot, a pilot that won't stay lit usually means a worn thermocouple or a draft across the burner compartment. On newer furnaces the hot-surface igniter is a wear part that cracks and stops glowing. Both are routine repairs, but the igniter is fragile and the pilot involves gas, so most homeowners leave them to a technician.

Water pooling around a high-efficiency furnace

Condensing furnaces produce water as they run and drain it through a small trap and hose. Water on the floor means the condensate trap or drain line is clogged, the condensate pump has failed, or the inducer motor housing is cracked. A clogged trap can also shut the furnace down through the pressure switch, so this is worth fixing before it becomes a no-heat call.

Heat pump systems that stop heating

If your home is heated by a heat pump with a furnace or electric strip as backup, the symptoms overlap but the fixes differ: ice on the outdoor unit, a reversing valve stuck in cooling, or backup heat that never kicks in. See heat pump not heating for the checks that apply to those systems.

Safe homeowner checks

These steps need no tools and keep you away from gas and line voltage. Stop at any point where something looks, sounds or smells wrong.

1. Thermostat. Set it to HEAT, raise the setpoint several degrees above room temperature, and replace the batteries if it has them. Set the fan to AUTO, not ON.
2. Power. Check the furnace switch (near the unit or at the top of the basement stairs) and the furnace breaker in the panel. Reset a tripped breaker once; if it trips again, stop.
3. Filter. Pull the filter and hold it up to a light. If you can't see light through it, replace it. A clogged filter is behind a large share of overheating and short-cycling calls.
4. Furnace door. Make sure the blower compartment door is fully seated so the safety switch closes.
5. Gas supply. Confirm the shutoff valve on the pipe to the furnace is open and that the stove or water heater still gets gas. Don't go further than looking at the valve handle.
6. Vents and returns. Open every supply register and clear furniture and rugs off return grilles. Closing vents in unused rooms raises pressure and heat inside the furnace.
7. Intake and exhaust pipes. On a high-efficiency furnace, check the two white PVC pipes outside for snow, ice, leaves or a nest. Clear only what you can reach from the ground.
8. Condensate drain. If there's a small pump near the furnace, make sure it's plugged in and its hose isn't kinked.

Before the cold season the winter furnace prep checklist covers the same items plus the things worth doing in October rather than in January.

Stop and call a professional when

• You smell gas. Leave first. Call your gas utility's emergency line or 911 from outside. Don't flip switches, use phones indoors, or open the garage door with the opener.
• A carbon monoxide alarm sounds or anyone in the home has headaches, dizziness or nausea while the furnace runs. Get out and call for help; have the furnace and venting inspected before using it again.
• The burner flame is yellow, orange or flickering instead of steady blue, or there's soot or rust around the burner compartment or vent pipe.
• The breaker trips again after one reset, or there's a burning-plastic or electrical smell that doesn't clear after the first run of the season.
• The furnace bangs at startup or makes grinding or screeching noises.
• The furnace keeps shutting off after you've replaced the filter and opened the vents.
• Anything involves the gas valve, igniter, flame sensor, control board or heat exchanger. These parts are inside the burner compartment and are tested with the furnace live.
• Water is near the furnace electrical connections or the panel. Don't step in it.

What to tell the technician

The more specific you're on the phone, the more likely the technician arrives with the right part. Have these ready:

• Fuel type: natural gas, propane, oil or electric, and whether a heat pump is part of the system
• The brand and model number from the label inside the furnace door, and roughly how old the furnace is
• Whether it's a high-efficiency (condensing) furnace with white PVC pipes or a standard furnace with a metal flue
• The exact symptom: no response, blows cold, short cycles, won't light, loud noise, runs nonstop, water on the floor
• What the furnace does when the thermostat calls for heat: inducer fan starts, igniter glows, burners light, blower runs, and where in that sequence it stops
• Any blinking light code on the control board (visible through the sight glass in the door) and how many flashes
• When it started and what changed first: a storm, a power outage, a new thermostat, a filter change
• What you have already tried: new filter, breaker reset, thermostat batteries
• Where the furnace is (basement, attic, crawl space, closet) and whether access is tight

How the service works

Describe the problem to an independent local heating company. A short automated prompt plays first, and then you're connected. You call, describe what is happening, and the call is routed to an independent contractor who serves your area and nearby towns. The pro asks a few questions, looks at the furnace and explains your options; you decide whether to hire. LocalRepairLine doesn't perform repairs and doesn't employ the contractors. We are a referral service, not a contractor.

Repair or replace: how heating contractors think about it

Igniters, flame sensors, capacitors, pressure switches, limit switches, blower motors and control boards are routine repairs on a furnace whose heat exchanger is sound. A cracked heat exchanger changes the conversation, because it lets combustion gases into the air stream and the part is the core of the furnace. An older furnace with a second major fault in one season, or one that can't keep the house warm on a normal winter day, is usually weighed against replacement. The technician who inspects it will lay out both paths; the decision stays with you. If you're already leaning toward a new unit, see furnace replacement.

Frequently asked questions

Furnace Repair by city

Choose your city for notes on local winters, common furnace faults in that area, and the number to reach an independent heating contractor who serves it.

Ohio

• Furnace Repair in Akron, OH
• Furnace Repair in Cincinnati, OH
• Furnace Repair in Cleveland, OH
• Furnace Repair in Columbus, OH
• Furnace Repair in Dayton, OH
• Furnace Repair in Springfield, OH
• Furnace Repair in Toledo, OH

Michigan

• Furnace Repair in Grand Rapids, MI
• Furnace Repair in Kalamazoo, MI
• Furnace Repair in Lansing, MI

Indiana

• Furnace Repair in Fort Wayne, IN
• Furnace Repair in South Bend, IN

Pennsylvania

• Furnace Repair in Philadelphia, PA
• Furnace Repair in Pittsburgh, PA

Delaware

• Furnace Repair in Dover, DE
• Furnace Repair in Newark, DE
• Furnace Repair in Wilmington, DE

Colorado

• Furnace Repair in Denver, CO

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