Furnace high limit switch codes by brand

A tripped high limit means the furnace got too hot. The codes below say so on nine different brands, and the cause is almost never the switch itself.

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

15 codes across 9 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	11 red flashes	Limit switch open due to blower failure
Goodman	4 red flashes	Open limit switch
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 251	Primary limit switch open
Lennox	Alert code 274	Primary limit switch open more than three minutes — Watchguard
Rheem	3 blinks	Limit switch open
Trane	4 flashes	Open high limit device
York	11 red flashes	Limit switch open more than five minutes — blower failure
York	4 red flashes	Open high limit switch

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.

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.