HVAC Code Lookup

Goodman Furnace Code 4

WarningShown as: 4 flashes, then a pause, repeating

Open limit switch. The furnace overheated and the high limit (or auxiliary limit) tripped. The blower keeps running to cool the heat exchanger. This is almost always an airflow problem.

Manual wording: “Open Main or Auxillary Temperature Limit Switch”

Documented for: Goodman GMS8, GMH8, GDS8, GDH8, GHS8, GME8, GMES80, GCES80, GMSS92, GMSS96, GCSS96 (single red diagnostic LED)

Likely causes, most common first

  1. Insufficient conditioned air over the heat exchanger
  2. Blocked filters
  3. Restrictive ductwork
  4. Improper circulator blower speed or a failed circulator blower
  5. Faulty primary or auxiliary limit switch
  6. Loose or improperly connected wiring

What you can safely check yourself

  • Check the air filter and replace it if it is dirty - this is the number one cause of a 4-flash code
  • Open all supply registers and make sure furniture, rugs or boxes are not blocking them
  • Make sure the return air grille is not blocked or covered
  • Check that any humidifier bypass damper is set correctly for the season

When to call a technician

If the code returns after a clean filter and open registers, the limit is tripping for a reason a technician must find - a failing blower, a restricted duct system, or a cracked heat exchanger. Never jumper or bypass a limit switch.

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

Sources

Other Goodman codes