The usual suspects
Fan set to ON instead of AUTO
ON blows room-temperature air between heat cycles all day. AUTO only blows when there’s actual heat. The free fix.
A dirty flame sensor
The furnace lights, runs 10 seconds, shuts off, blows cold. A $10 part’s worth of buildup causes a huge share of winter calls.
Ignition failure
A worn igniter or pilot problem means burners never light — the blower runs, nothing warms it.
An overheat safety tripping
A clogged filter overheats the furnace; the limit switch cuts the burners and runs the fan cold to cool down. Repeatedly.
No heat is a today problem.
Furnace no-heat calls get priority in the cold months — most ignition and sensor fixes happen in one visit.
Book My Same-Day Visit60 seconds online · or call (206) 486-6373
Worth trying first (5 minutes, free)
- 1
Thermostat: HEAT, fan on AUTO, set 3°F above room temperature.
- 2
Swap a dirty filter — overheat lockouts usually start here.
- 3
Power-cycle once: furnace switch off 30 seconds, then on. One try.
- 4
Listen at startup: clicking with no whoosh of ignition points at the igniter or flame sensor.
Still not working? Then it’s a technician job — and the sooner it’s booked, the sooner the house is comfortable again. Book the visit →
Stop and book a pro if…
- A gas smell — leave the house first, then call PSE’s gas emergency line.
- Your CO alarm sounds — get everyone out, then call 911.
- It lights, dies in seconds, repeats — flame sensor or venting; stop cycling it.
- The blower runs non-stop cold even with the thermostat OFF.
Why homeowners hand it to us
- You approve the price first. Upfront quote before a single screw turns.
- Same-day service. Book in a minute, hear from a tech within 1 business hour.
- 500+ jobs done by 4.9★ rated, professional technicians.
- Fixed right, guaranteed. If it’s not right, we make it right.
Quick answers
Why does it blow warm, then cold, then warm?
That rhythm is an overheat or flame-sense cycle: heat, safety trip, cool-down, retry. It will not fix itself — but it’s usually a filter, sensor cleaning, or airflow fix, not a new furnace.
Is cold air ever dangerous?
The air itself, no — but repeated safety lockouts and any burning or gas smell mean the furnace is asking for help. And every home with a gas furnace should have a working CO alarm — that’s non-negotiable.
Can you fix it today?
Igniters, flame sensors, filters and limit switches are on-truck parts. Book online — a tech reaches out within 1 business hour with the price upfront.
Done guessing?
Cold house tonight or warm house tonight — book now and a tech reaches out within 1 business hour.
Book My Same-Day Visit60 seconds online · or call (206) 486-6373
More: all problems · heating service · AC service · 24/7 emergency