Goodman Furnace 4 (red LED) error code
The primary limit switch opened, which means the furnace got too hot inside the heat exchanger. The burners shut off while the blower keeps running to cool things down.
Also shown as: 4 red flashes, four red flashes, fault code 4 red, limit circuit open, high limit fault
Last updated: September 30, 2026
What causes the 4 (red LED) error?
- Dirty or clogged air filter
- Blocked supply registers or restrictive ductwork
- Blower speed set too low
- Failing blower motor
- Faulty limit switch
How to fix Goodman 4 (red LED) — step by step
Work through these in order, from simplest and safest first. Stop as soon as the code clears.
- Replace the air filter
A clogged filter is the most common cause. Install a clean filter of the correct size and type. - Open registers and clear returns
Make sure every supply register is open and return grilles are not blocked by furniture, rugs, or curtains. - Call a technician if it repeats
If the code comes back with a clean filter, the blower, ductwork, or the limit switch itself needs professional testing.
When to call a technician
- The code returns with a new filter and open vents
- The blower does not run during the fault
- You notice a burning smell or scorched marks near the furnace
Frequently asked questions
Is an overheating furnace dangerous?
It can be. Repeated overheating stresses the heat exchanger, which can eventually crack and leak carbon monoxide. Take recurring limit faults seriously.
Why does the blower keep running?
That is normal — the control runs the blower to cool the heat exchanger after a limit trip.
Sources
Every meaning and fix above was checked against official manufacturer documentation:
FixCode provides general troubleshooting information only — not professional repair advice. If you are unsure about any step, stop and call a qualified technician. Repairs done incorrectly can be dangerous and may void your warranty.