What does Intertherm code 4 Blinks mean?
Intertherm furnace code 4 Blinks means the high-temperature limit switch is open on the supported control family. Confirm the model number and diagnostic chart inside the furnace door before replacing parts.
What causes Intertherm code 4 Blinks?
- A dirty or overly restrictive air filter
- Closed or blocked supply and return vents
- A blower, limit switch, or airflow problem
Can I troubleshoot Intertherm code 4 Blinks?
- Turn the furnace off and replace a dirty filter with the size and type specified for the system.
- Open all supply registers and make sure return grilles are not blocked before trying one reset.
How much does Intertherm code 4 Blinks cost to fix?
A limit switch replacement typically costs between $150 and $750 nationally.
When should I call a technician?
Call a technician if the limit code returns; repeated overheating can damage the furnace.
Symptoms this code causes
Sources and model scope
Fault codes vary by model and control board. Confirm the diagnostic chart inside your furnace panel or the official manual before acting.
Scope used here: Nortek single-stage condensing furnaces using the documented Emerson integrated control.
- Nortek Global HVAC: Single Stage Condensing Gas Furnaces — Installation Instructions
1041594D · Nortek single-stage condensing gas furnaces using the documented Emerson integrated control; manufactured-home models and older boards may differ.
Compiled by Warmlo Editorial · Reviewed August 2026
This is general information, not professional advice. Gas, electrical, and combustion repairs can be dangerous — when in doubt, call a licensed technician.