Heating
Furnace repair
When a gas furnace won't heat, the cause is usually a dirty flame sensor, a failed igniter, a blocked filter or a tripped pressure switch. A licensed technician reads the furnace's error code, tests the safety controls, and checks for carbon monoxide before returning it to service.
- Licensed local HVAC contractor
- Diagnosis and price before work
- Same-day appointments when a local contractor has an opening
- Free to call, no obligation
Modern furnaces flash a diagnostic code on a small LED inside the blower door. Count the flashes and match them to the chart on the panel; it narrows the problem fast and helps the technician arrive with the right part.
If you smell gas, leave the house and call the gas utility's emergency line from outside. If a carbon monoxide alarm sounds, get everyone out and call 911. Those are not furnace-repair calls until the utility or fire department clears the home.
Furnace Repair at a glance
- Category
- Heating
- Urgent service
- Often available, depending on local contractors
- Who does the work
- An independent, licensed HVAC contractor
- Quote
- Given after diagnosis, before work starts
Signs you need furnace repair
- Furnace starts, then shuts off within a minute
- Blower runs but only cold air comes out
- Clicking with no ignition
- Error code flashing on the control board
- Yellow or flickering flame instead of steady blue
What the technician does
- 1
Safety first
Gas pressure, venting and a carbon monoxide test before anything is restarted.
- 2
Read the code
The control board's fault history points to the circuit that failed.
- 3
Test components
Igniter resistance, flame-sensor current, pressure switch and inducer motor are measured, not guessed.
- 4
Repair and verify
After the fix the furnace runs a full cycle while temperature rise and venting are checked.
What affects the cost
Prices are set by the contractor after diagnosis. These are the factors that move the number most:
- The failed part (flame sensor cleaning vs. control board or inducer motor)
- Furnace age and parts availability
- Venting or condensate problems on high-efficiency units
- After-hours scheduling during cold snaps
Safe to check yourself
- Replace the filter
- Check that the furnace switch and breaker are on
- Make sure outdoor PVC intake and exhaust pipes aren't blocked by snow
- Note the LED flash code
Leave to a pro
- Bypassing a limit or pressure switch
- Adjusting gas pressure
- Running a furnace with a cracked heat exchanger or a CO alarm sounding
Furnace Repair FAQ
Why does my furnace turn on and then shut off?
Short cycling on startup is most often a dirty flame sensor that can't prove the flame. A clogged filter, blocked vent pipe or failing pressure switch can cause the same pattern.
Is a furnace with no heat an emergency?
It becomes urgent when indoor temperatures drop toward freezing, when there are infants, elderly or sick people in the home, or when pipes are at risk. A gas smell or CO alarm is always an emergency for the utility or 911 first.
How long do furnaces last?
Most gas furnaces last 15–20 years with regular maintenance. Past that age, a heat exchanger crack or major part failure often makes replacement the better value.
What do the blinking lights on my furnace mean?
The blinking LED on the control board is a diagnostic code. Count the flashes and match them to the chart inside the blower door; common codes point to pressure switch, flame sensing or limit faults.
Why does my furnace blow cold air?
Cold air usually means the burners didn't light or shut off early, often from a dirty flame sensor, failed igniter or safety switch. A thermostat set to fan On can also blow unheated air between cycles.
Why is my high-efficiency furnace leaking water?
High-efficiency furnaces make condensate. A clogged condensate trap or line, or a frozen drain outdoors, can cause leaks and shut the furnace down.
What does a cracked heat exchanger mean?
A cracked heat exchanger can let combustion gases mix with house air. A technician should confirm it with an inspection, and most furnaces with a cracked heat exchanger are replaced rather than repaired.
How can I stay warm until the furnace is fixed?
Close off unused rooms, use space heaters safely away from anything that burns, and open cabinets under sinks on outside walls to keep pipes from freezing.
Last reviewed . General information, not a diagnosis of your system.
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