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 Seattle, WA: 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 Seattle, WA
- Seattle Steam Co · Puget Sound Plaza, 1325 4th Ave #1440, Seattle, WA · +12066236366
- Warren Company · 500 Union St Ste 900, Seattle, WA · (206) 749-9484
- US HVAC Home Service Seattle · 300 Pine St Ste 100, Seattle, WA · (253) 793-1154
- MM Comfort Systems · 800 5th Ave 101 463, Seattle, WA · 2065429100
- Dorse and Company · 5000 1st Ave S, Seattle, WA · +12062842610
- Mighty Energy Solutions · 2910 1st Ave S Ste 201, Seattle, WA · +12068801558
- United Systems Mechanical · 1400 Airport Way S Ste 202, Seattle, WA · +12069336036
- Local Hvac Expert Seattle · 3250 Airport Way S, Seattle, WA · +12065651003
Get free quotes from Seattle, WA 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.