Troubleshooting
10 Signs Your Furnace Needs Repair
Quick answer
The most important furnace warning signs are a yellow or flickering burner flame, any carbon monoxide alarm, scraping metal sounds, and repeated breaker or limit trips, all of which warrant shutting the system down immediately. Rising bills, short cycling, cold spots, and frequent ignition failures mean schedule repair soon.
Shut it down now signs
A few symptoms indicate genuine safety hazards. Turn the furnace off at the switch and call for same day service if you notice any of these.
- Carbon monoxide alarm activation, or family members with unexplained headaches and nausea that improve away from home
- Yellow, orange, or lazily flickering burner flames instead of steady blue, indicating incomplete combustion
- Strong aldehyde or exhaust smell near the furnace, or soot streaks around the cabinet and vents
- Metal on metal scraping or banging from the blower area
- The smell of gas: leave the house first, then call the gas utility before any contractor
Schedule repair soon signs
These symptoms will not hurt anyone today, but each one compounds into bigger bills the longer it runs.
- Short cycling, with the furnace starting and stopping every few minutes, which wears ignitors and heat exchangers fast
- Ignition failures, clicking without light off, or the furnace trying several times before catching
- Heating bills rising noticeably against similar weather last year
- Uneven heating with rooms that never warm up, often airflow or ductwork trouble
- Squealing or rumbling that changes with blower speed, indicating belt or bearing wear
- The furnace is past 15 years old and needing repairs annually
What common furnace repairs cost
Furnace repairs are generally cheaper than AC repairs, and catching them early keeps them that way.
| Repair | Typical cost |
|---|---|
| Ignitor replacement | $150 to $400 |
| Flame sensor cleaning or replacement | $80 to $250 |
| Blower motor | $400 to $1,500 |
| Control board | $400 to $1,200 |
| Inducer motor | $300 to $900 |
| Gas valve | $300 to $800 |
| Heat exchanger | $1,500 to $3,500, usually replace the furnace instead |
Frequently asked questions
Why does my furnace turn on and off every few minutes?
Short cycling usually comes from an overheating limit trip caused by a clogged filter or blocked vents, a dirty flame sensor dropping the flame signal, or an oversized furnace. Change the filter first; if cycling continues, a technician can clean the sensor and check limits in one visit.
Is a 20 year old furnace safe?
It can be, but only with annual professional inspection of the heat exchanger and combustion. Heat exchanger crack risk rises sharply past 15 years, and a crack can introduce carbon monoxide into your air. Working CO detectors on every level are essential with any aging furnace.
Why is my furnace blowing cold air?
Common causes are a thermostat fan set to On instead of Auto, a pilot or ignition failure, a clogged filter tripping the high limit, or a condensate blockage on high efficiency models. If cycling the thermostat and changing the filter do not fix it, the ignition system likely needs service.
Related guides
- Why Is My Furnace Making Noise?What furnace noises mean, from booms and bangs to squeals and rumbles, which are harmless and which demand immediate shutdown.
- Winter HVAC ChecklistMid winter heating care, cold snap protocols, frozen pipe prevention, and heat pump winter behavior explained.
- What Does HVAC Repair Cost?Complete 2026 HVAC repair pricing: national averages by repair type, what drives the price up or down, and how to know a quote is fair.
- Emergency HVAC ChecklistWhat counts as an HVAC emergency, what to do in the first ten minutes, emergency service costs, and how to stay safe until help arrives.