American Standard · Furnace / HVAC
4 flashes Limit switch open
What this code means
The furnace overheated and the high-limit switch cut the burners as a safety measure.
Most likely causes
- Dirty air filter
- Closed supply vents
- Failing blower motor
What to try first
Replace the air filter and open closed vents throughout the house.
Good news: this one is often fixable without a service call. If it persists after the steps above, have it looked at.
Find the part on Amazon →FAQ
What does American Standard error code 4 flashes mean?
Limit switch open. The furnace overheated and the high-limit switch cut the burners as a safety measure.
Can I fix American Standard code 4 flashes myself?
Often, yes. Replace the air filter and open closed vents throughout the house.
What causes American Standard code 4 flashes?
The most common causes are: dirty air filter; closed supply vents; failing blower motor.
Other American Standard furnace codes
All American Standard furnace error codes →
Other furnace brands: Trane · Carrier · Lennox · Goodman · Amana · Rheem · Bryant · Generic · Nest
This information may contain errors or not apply to your exact model — always double-check it against your appliance's own manual before acting. If there's any chance of a gas, fire, electrical, carbon monoxide, or other safety hazard, stop and call a licensed professional or the appropriate agency (e.g. your gas utility) instead of relying on this page alone.