Heating
Furnace Repair
A furnace that quits in January is an emergency, but most furnace failures announce themselves first: new noises, short-cycling, a yellow burner flame, or the smell of something wrong. Repair starts with safety — heat exchanger integrity, gas connections, venting, and carbon monoxide — then moves to the failed component. Any tech who skips the combustion safety checks is not doing the job.
Furnace Repair: at a glance
- What it is:
- Diagnosis and repair of gas, oil, or electric furnaces — ignition failures, no heat, short-cycling, strange smells, and safety shutdowns.
- When you need it:
- When the furnace is under ~15 years old and the failure is a single component (ignitor, flame sensor, blower motor, control board).
- The key decision:
- Cracked heat exchangers and repeated major failures are replacement signals, not repair ones. Ask the tech to show you the failed part and explain whether the repair extends the system's real life.
Key facts
| Typical timeline | Same visit for common failures; safety issues take priority |
|---|---|
| Key risk | Cracked heat exchanger — a safety issue, not a repair candidate |
| Relative scope | Small — one failed component |
| Best for | Furnaces under ~15 years with a single, explainable failure |
Typical ranges for the material category — your home, climate, and installer quality move real results.
Do this first
- Check the thermostat (heat mode, set above room temp), the furnace switch, breaker, and gas valve position.
- Replace a clogged filter — restricted airflow overheats furnaces and trips safety limits.
- If you smell gas, leave and call the gas utility or 911 — do not troubleshoot a gas leak yourself.
- Note the furnace's behavior: won't start, starts then stops, runs but blows cool — the pattern guides diagnosis.
What the crew does
- Verify the basics: thermostat, power, gas supply, and filter before diagnosing deeper
- Inspect the heat exchanger for cracks — the safety-critical check on every no-heat or old-furnace call
- Test ignitor/hot surface ignitor, flame sensor, and pressure switches — the most common failure points
- Check gas pressure and combustion, and venting for blockages or deterioration
- Test for carbon monoxide at the furnace and in the living space
- Clean the flame sensor and burners, which resolves a large share of 'won't stay lit' calls
Common questions
It means the furnace must be replaced, not repaired — a cracked heat exchanger can leak carbon monoxide into your home's air. This is the one furnace diagnosis that ends the conversation about repair. A reputable tech will show you the evidence and shut the furnace down.
Short-cycling has several causes: an overheating furnace tripping its high limit (often a clogged filter or failing blower), a faulty flame sensor, or an oversized furnace. It wastes energy and wears parts fast — get it diagnosed rather than living with it.
Weigh age, repair cost, efficiency, and safety. Past about 15–20 years, major repairs deserve a replacement comparison — especially if the heat exchanger is involved. A cracked heat exchanger always means replacement.
Related topics
Furnace Repair by state
Local climate changes the right material and details. Pick your state for furnace repair guidance tuned to local conditions.