Why is my furnace not heating?
A furnace that won't heat is most often a dirty filter choking airflow, a failed igniter, or a thermostat problem — in that order of cheapness. A furnace that starts, runs a minute, then stops is usually a dirty flame sensor. True no-heat in deep cold justifies the after-hours call; a mild-weather failure usually doesn't.
Likely causes
- Clogged filter — Restricted airflow overheats the furnace until the safety switch shuts it down.
- Failed igniter — Modern furnaces light with a hot-surface igniter that cracks every 5–7 years. Clicking with no flame points here.
- Dirty flame sensor — The furnace lights, runs a minute, and quits — the sensor can't prove flame, so it shuts down safely.
- Thermostat or power issue — Dead thermostat batteries, a tripped breaker, or an open furnace door switch — check before you pay for a visit.
What you can check yourself
- Replace the filter, and confirm the thermostat is on 'heat' with fresh batteries if it uses them.
- Check the breaker and the furnace's own power switch (it looks like a light switch, usually near the unit).
- Make sure the furnace access door is fully closed — many units won't run with the door switch open.
Typical cost
Typical repairs in Chicago, IL: service call $100–$250; igniter $150–$350; flame sensor cleaning/replacement $150–$300; blower motor $400–$800.
When to call a pro
Gas smell, a carbon monoxide alarm, or a furnace that short-cycles with a burning smell — leave and call from outside. Otherwise, no heat below ~40°F with kids or elderly at home counts as urgent.
HVAC pros in Chicago, IL
- Chicago Heating and Cooling · 111 W Jackson Blvd, Chicago, IL · +17736445920
- Heatmasters · 208 S La Salle St, Chicago, IL · +13126249324
- Tabor's Complete Comfort Mechanical, LLC · 1449 S Michigan Ave,, Chicago, IL · (773) 715-3860
- Westside Mechanical Group · 311 S Wacker Dr Ste 5350, Chicago, IL · 3123003370
- ClearSky Duct Solutions · 161 N Wacker Dr, Chicago, IL · +18722553529
- Better Air Chicago · 233 S Wacker Dr 84th Fl, Chicago, IL · 3127657485
- Green Air USA · 556 W Lake St Ste 227, Chicago, IL · (773) 895-8500
- Chicago Heating & Cooling · 350 N La Salle Dr Fl 9, Chicago, IL · 13128525152
Get free quotes from Chicago, IL pros →
Data by Servik — verified local pros from official license records and public sources. Cost figures are typical ranges, not quotes; a pro's written estimate is the real number.