From the hallway, a furnace that will not heat looks the same no matter what broke. Inside the cabinet, though, the sequence is strict: inducer on, pressure switch closed, igniter glowing, gas valve open, burners lit, flame proven, and finally the blower moving heat through the ducts. Diagnosis is mostly a matter of finding where that chain breaks. In Longmont homes, it tends to be the same handful of culprits: a flame sensor coated in oxide, a hot surface igniter cracked by thermal cycling, a pressure switch held open by a tired inducer or a plugged condensate trap, or a control board with a burned relay.
When the AC quits in summer, see AC Repair.
Warning Signs for Furnace Repair
Spotting the early warning signs lets you act before the problem gets expensive. These are the signals our technicians see most often:
- A fan that keeps running while the registers blow cool air
- The furnace clicks and glows but the burners never light
- A pilot or burner flame that is lazy yellow instead of crisp blue
- Grinding or high-pitched squeals from the blower
- Booming or banging at light-off from delayed ignition
- Soot, rust, or moisture near the furnace cabinet or vent pipe
- Burners light, run a few seconds, then shut down repeatedly
- A furnace that shuts off every few minutes before the house warms up
Don't Wait for a Total Failure
Most HVAC failures start small, a weak capacitor, a squealing blower, a system that runs a little longer each week. If you notice any of these signs, call (970) 602-4958 for a prompt inspection.
