Symptoms this service addresses
- Furnace won't turn on or thermostat shows no power
- Burners light but cold air still blows from the vents
- Furnace short cycles — fires up briefly then shuts off
- Loud bangs, rumbles, or whistles at startup
- Yellow burner flame instead of steady blue
- Carbon monoxide detector going off — shut the system off and ventilate
- Pilot or ignitor failing on a high-efficiency model
What the service involves
- Diagnostic check of thermostat call, gas valve, and ignition sequence
- Inspection of the flame sensor, ignitor, and pressure switch
- Verification of venting and condensate drain on high-efficiency units
- Combustion check and visual inspection of the heat exchanger
- Replacement of failed parts and a verified heat cycle before leaving
What affects cost and timing
- Which component failed — flame sensors and ignitors are inexpensive; control boards and inducers are not
- Furnace age and whether parts are still readily available
- Single-stage vs two-stage or modulating equipment
- Whether venting or gas-line work is required
- Accessibility — attic and crawlspace installs add labor time
When it's urgent
- No heat in sub-freezing weather, especially with vulnerable household members
- Any sign of carbon monoxide — yellow flame, detector alarm, headaches in the home
- Burning or electrical smell from the furnace
- Pipes at risk of freezing if heat is out overnight
What to check before requesting help
- Confirm the thermostat is set to Heat and the setpoint is above room temp
- Replace the air filter — clogged filters trip high-limit switches
- Check the furnace switch (looks like a light switch) is on
- Confirm the breaker hasn't tripped and gas service is on
- Note the system brand, model, and any blinking LED error codes
FAQ
The most common causes are a tripped high-limit switch, a dirty flame sensor, a failed ignitor, the thermostat set to fan-on instead of auto, or burner flame loss. With a gas furnace, never bypass safety switches — they're protecting the heat exchanger.