Furnace Error Code Lookup — Start Here
Furnace fault codes are usually shown as blinking LEDs, two-digit board codes, or thermostat alerts. This page is your fast lookup hub for the most common furnace brands and the faults technicians see most often: pressure switch issues, limit trips, ignition failures, flame sensing, blower faults, and rollout safety trips.
Common Furnace Fault Patterns
| Fault Type | What It Usually Means |
|---|---|
| Pressure switch open | Inducer draft problem, blocked vent, condensate issue |
| Limit switch open | Overheating from airflow restriction |
| Ignition lockout | Gas, igniter, or flame sensor problem |
| Flame sense fault | Dirty flame sensor or bad grounding |
| Blower fault | PSC capacitor, ECM module, or airflow issue |
| Rollout switch open | Serious combustion problem, stop and inspect |
Brand Hubs Covered
- Carrier and Bryant
- Goodman and Amana
- Lennox
- Trane and American Standard
- York and Coleman
- Heil, Tempstar, Comfortmaker, ICP brands
- Rheem and Ruud
Step-by-Step Fix
- Read the exact flash count or code.
- Check the filter and airflow first — This solves a surprising number of limit faults.
- Watch the ignition sequence — Inducer, igniter, gas valve, flame prove.
- Clean the flame sensor before replacing expensive parts.
- Treat rollout faults as safety faults, not nuisance codes.
Parts Often Needed
| Part | Notes |
|---|---|
| Flame sensor | Amazon | Cheap and commonly dirty |
| Hot surface igniter | View on Amazon | Fragile, common wear part |
| Pressure switch | View on Amazon | Check tubing before replacing |
| Blower capacitor | Amazon | Common on PSC motor furnaces |
| Air filter | View on Amazon | Low-cost first fix |
When to Call a Pro
If the code points to rollout, heat exchanger concerns, gas valve issues, or persistent lockouts after basic cleaning and filter replacement, call a licensed HVAC technician. Some furnace faults are safety issues, not DIY maintenance items.