Troubleshooting
Furnace Not Turning On? 8 Things to Check Before You Call
A furnace that won't fire up is alarming, especially on a cold Bellevue morning, but a surprising number of "dead" furnaces are brought back to life in a couple of minutes with no tools. Before you book a service call, run through these eight checks in order. If you get to the end and still have no heat, that's exactly when to call a pro.
1. Check the thermostat
It sounds obvious, but it's the #1 cause of "no heat" calls that turn out to be nothing. Make sure it's set to HEAT (not COOL or OFF) and that the target temperature is set several degrees above the current room temperature. If the screen is blank, replace the batteries, a dead thermostat can't ask the furnace for heat.
2. Set the fan to AUTO, not ON
If your thermostat fan is set to "ON," the blower runs constantly, even when the furnace isn't heating, so you feel cool air and think it's broken. Switch the fan to "AUTO" so it only runs during a heating cycle.
3. Check the air filter
A badly clogged filter is one of the most common reasons a furnace shuts itself down. Restricted airflow makes the furnace overheat and trip its safety limit. Pull the filter, if you can't see light through it, replace it. This alone fixes a lot of no-heat calls, and it's the single best habit for furnace health.
4. Check the breaker
Head to your electrical panel and look for a tripped furnace breaker (it'll sit between ON and OFF, or be flipped to OFF). Flip it fully OFF, then back ON. Important: if it trips again right away, stop, don't keep resetting it. A repeatedly tripping breaker is a real fault that needs a technician.
5. Check the furnace power switch
Most furnaces have a switch nearby that looks exactly like a regular light switch, often on or near the unit itself. It's easy for it to get bumped off (or flipped by someone who thought it was a light). Make sure it's ON and give the furnace a few minutes to start its sequence.
6. Make sure the furnace door is fully closed
Furnaces have a safety interlock, a door switch, that won't let the unit run unless the front panel is properly seated. If the panel was removed (say, to change a filter) and not clicked fully back in place, the furnace simply won't start. Press it firmly until it seats.
7. Check the condensate drain (high-efficiency furnaces)
High-efficiency (90%+) furnaces produce water as they run, and they drain it away. If that drain or its float switch clogs, the furnace shuts off to avoid an overflow. If you see standing water near the unit or a full drain pan, that's likely your culprit, and a job for a pro to clear safely.
8. Look (and listen) for the ignition sequence
Turn the heat up and watch the furnace. A healthy gas furnace runs a sequence: you'll hear the inducer motor spin up, then a click and a glow as the igniter heats, then the burners light, then the blower kicks in. If it clicks and tries but never lights, or lights and then shuts off after a few seconds, that points to a dirty flame sensor or a failing igniter, both common, both affordable, and both a job for us.
Still no heat?
If you've worked through all eight and your furnace still won't run, the problem is internal, a sensor, igniter, control board, motor or gas-valve issue, and it's time to call. The good news is that the most common internal failures are inexpensive and same-visit fixes. We hold same-day repair slots across Bellevue and the Eastside, and run an after-hours line for evening and weekend no-heat emergencies.