Furnace high limit switch codes by brand

A tripped high limit means the furnace got too hot. Every brand has codes for it, and the cause is almost never the 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 the high limit switch does

The high limit is a temperature-sensing switch in the heat exchanger compartment that opens when the air leaving the furnace exceeds a set temperature. It is normally closed, wired in series with any other limits, and opening it shuts off the gas valve while leaving the blower running to clear the heat.

Why one part produces several different codes

A limit that opens is reporting a real overheat, and the overheat is nearly always a lack of airflow across the heat exchanger — a clogged filter, closed or blocked registers, an undersized or crushed return duct, a failed or slow blower motor, or a blower wheel packed with dirt. Replacing a limit switch that is doing its job correctly leaves the overheat in place and removes the protection against it.

Every high limit switch code on this site

17 codes across 11 control families. The meaning is the manufacturer's, from the document listed at the foot of each code page.

Brand	Code	What it reports
Armstrong	7 flashes	Primary or secondary limit open, or Watchguard after three minutes open
Goodman	4 flashes	High limit switch is open — the furnace is overheating
Goodman	6 flashes	Rollout limit open, or control module fuse blown
Goodman	E3	High limit switch is open — the furnace is overheating
Goodman	4 red flashes	Open limit switch
Goodman	11 red flashes	Limit switch open due to blower failure
Heil	4 flashes	Limit switch string is open
Heil	7 flashes	Soft lockout — limit trips taking longer than two minutes to reset
Lennox	Alert code 200	Rollout limit switch open
Lennox	Alert code 250	Primary limit switch open
Lennox	Alert code 274	Primary limit switch open more than three minutes — Watchguard
Lennox	E250	Limit switch circuit open
Rheem	3 blinks	Limit switch open
Trane	4 flashes	Open high limit device
Trane	E09	Open inducer limit switch or condensate pressure switch
York	4 red flashes	Open high limit switch
York	11 red flashes	Limit switch open more than five minutes — blower failure

Before you work on it

Repeated limit trips overheat the heat exchanger, which is the component whose failure lets combustion gases into the supply air. A furnace that keeps tripping on limit needs the airflow problem found, not the limit replaced.

What the fixes cost

The furnace repair cost guide lists a limit switch at $150–350, annotated with this page's own thesis: find why it tripped, not just the part. The realistic bills follow the causes. A meaningful share cost almost nothing — a clogged filter or closed registers found during the $75–150 diagnostic. The middle case is blower-side: a PSC blower's failed capacitor at $150–350, which the blower cost guide says any honest technician tests before condemning a motor, or the motor itself at $400–1,500. The tail risk is why deferral is expensive: repeated limit trips overheat the heat exchanger, and at $1,000–2,500+ the exchanger is usually the replace-the-furnace conversation.

Do it yourself or call someone?

Homeowner work on a limit code is exactly two items: a fresh filter and open supply registers. Both fix real cases, cost pocket change, and need no tools. The discipline is in what follows if the code returns anyway — stop resetting and book the visit, because each further trip is another overheat through the exchanger. Diagnosing weak airflow beyond the filter means blower amp draws and capacitor tests on live line voltage, with capacitors holding charge even after power-off; that half belongs to the technician.

Other parts

Sources

Every code meaning above comes from the manufacturer document behind its code page:

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.