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 Miami, FL: 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 Miami, FL
- New Duct Service Company · 1851 Delaware Pkwy, Miami, FL · +15612698633
- AC Repair Miami Pros · 3580 NW 54th St, Miami, FL · +17866864127
- Barrios Air Conditioning Inc · 3461 NW 48th St, Miami, FL · +13056370109
- Tri-County Mechanical Inc · 3305 NW 37th St, Miami, FL · 3052561858
- Ice Team Corporation · 3274 NW 38th St, Miami, FL · 17862566371
- Og Ac Distributor · 3235 NW 37th St, Miami, FL · +13056335144
- Navas Multiservices Corporation · 3050 NW 40th St, Miami, FL · 13053251077
- Nicot Air Conditioning Inc · 2385 Nw 70th Ave Unit A02, Miami, FL · 17862831366
Get free quotes from Miami, FL 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.