HVAC Code Lookup

Ruud Furnace Code 3

Soft lockoutShown as: 3 blinks of the green status LED, repeating

Limit circuit open. The high limit (or an auxiliary limit) has opened because the heat exchanger got too hot, which almost always means restricted airflow.

Manual wording: “3 Blinks - Limit circuit open”

Documented for: Standard furnaces with a green status LED, incl. RGRA/RGRB/RGTA/RGRS/RGTS/RGRT

Likely causes, most common first

  1. Dirty or clogged air filter restricting airflow
  2. Closed or blocked supply registers and return grilles
  3. Blower not running or running too slowly
  4. Faulty limit control or loose wiring

What you can safely check yourself

  • Check the air filter and replace it if dirty - this is the most common cause.
  • Open all supply registers and clear anything covering return air grilles.
  • Make sure the blower door is fully closed and seated.
  • Let it cool, then reset power once at the furnace switch.

When to call a technician

If three flashes come back after a clean filter and open registers, the blower, ductwork or limit control needs a technician. Never jumper or bypass the limit.

A Ruud furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.

Sources

Other Ruud codes