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 Austin, TX: 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 Austin, TX
- 24/7 AC Repair Austin · 704 San Antonio St., Austin, TX · 7372154475
- Classic Aire Mechanical, Inc. · 1108 Lavaca St Ste 110-487, Austin, TX · +15124478300
- Tex-air Heating & Air Conditioning · 506 Congress Ave, Austin, TX · +15125637505
- Gold Eagle Services · 501 Congress Ave Ste 150, Austin, TX · 8303023864
- RedHome HVAC Services · 823 Congress Ave Ste 150, Austin, TX · 5124027277
- Quick Cooling Inc. · 500 E 4th St #323, Austin, TX · 5129192193
- Hot Rod Mechanical · 3415 E 5th St, Austin, TX · +15123868686
- Green Leaf A/C and Heating · 1405 Clifford Ave, Austin, TX · 5126404790
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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.