Furnace overheats and trips the high limit

The furnace lights normally, runs for several minutes, then shuts the burners down while the blower keeps going. It is overheating, and the cause is almost never the limit switch itself.

Some of the faults listed here are gas-safety faults. Those ones involve the gas valve, the burner compartment, or the heat exchanger — the parts whose failure can put combustion products, including carbon monoxide, into the air the house breathes, and each carries this warning on its own page. Do not keep resetting a furnace that reports one of them in order to hold the heat on. Have it looked at by a licensed technician, and make sure there is a working carbon monoxide alarm on every level of the home, including the level the furnace is on. The conditions that mean stop now.

What is actually happening

The high limit is a normally-closed temperature switch in the heat exchanger compartment that opens when the air leaving the furnace exceeds a set temperature. Opening it cuts the gas valve while leaving the blower running to carry the heat away. A furnace that keeps tripping on limit is a furnace that is producing more heat than the airflow can remove.

What causes it

Nearly every cause is a lack of airflow: a clogged air filter, closed or blocked supply registers, blocked return grilles, an undersized or crushed return duct, a blower wheel packed with dirt, or a blower motor running slow or not at all. Several manufacturers publish a separate code specifically for a limit that opened because the blower failed, which is the same overheat with the cause already identified. Less common but real: an oversized furnace for the duct system, or a gas pressure set too high.

The codes that report this

13 codes across 10 control families. Each links to what that manufacturer says about it.

Brand	Code	What it reports
Armstrong	7 flashes	Primary or secondary limit open, or Watchguard after three minutes open
Carrier	Status code 13	Limit circuit lockout
Goodman	4 flashes	High limit switch is open — the furnace is overheating
Goodman	E3	High limit switch is open — the furnace is overheating
Goodman	11 red flashes	Limit switch open due to blower failure
Heil	6 + 4 flashes	Soft lockout — limit circuit opened during the run
Heil	7 flashes	Soft lockout — limit trips taking longer than two minutes to reset
Lennox	Alert code 250	Primary limit switch open
Lennox	Alert code 274	Primary limit switch open more than three minutes — Watchguard
Lennox	Alert code 295	Indoor blower motor overheating
Lennox	E274	Soft lockout — recycles exceeded, limit circuit opened
Rheem	3 blinks	Limit switch open
York	11 red flashes	Limit switch open more than five minutes — blower failure

Worth knowing

Replacing a limit switch that is doing its job leaves the overheat in place and removes the protection against it. Repeated limit trips stress the heat exchanger, and the heat exchanger is the component whose failure puts combustion gases into the supply air. Find the airflow restriction.

Other symptoms

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.

Error codes behind this symptom

If your furnace is flashing a code while doing this, these code families are the usual suspects: limit switch codes, blower motor codes. Look your exact code up from the brand index, and see the furnace repair cost guide for what the fix typically runs.