Trane furnace blinking 4 times: open temperature limit circuit

By Jason Dearmin · Last reviewed November 14, 2026 · How we check facts

What four flashes mean

Trane's installer guide 18-CH49D1-1 lists the IFC error flash codes. For 4 flashes the entry reads "Open Temperature Limit Circuit." That is the whole definition in Trane's table; it does not list individual causes for this code.

The same document says how to read the LED: a slow flash means normal with no call for heat, a fast flash means normal during a call for heat, continuous on means replace the IFC, continuous off means check power, and a numbered code is the count of flashes in a group.

How this compares with other brands

The condition is the same one Carrier calls status code 33 (limit circuit fault). Carrier's manual lists a dirty filter or restricted duct system, a restricted vent, a loose blower wheel, a defective blower motor or capacitor, excessive wind and a defective switch or connection as things to check. Goodman's manual explains that the primary limit guards against overheating from insufficient air passing over the heat exchanger. Those lists come from other manufacturers, so use them as background, not as Trane's diagnosis for your model.

What is safe to check

• Replace a clogged air filter.
• Make sure supply registers and return grilles are open and unblocked.
• Look from the ground at the outdoor vent and intake pipe ends for snow, ice or debris.

If four flashes return after that, have a technician look at the limit switches, the blower, and the airflow. Trane's installer guide itself warns to disconnect power before removing the blower door because of moving parts, and to label wires before disconnecting any control.

Safe homeowner checks for a Trane furnace blinking 4 times

1. Turn the thermostat offSet the thermostat to off so the furnace stops calling for heat.
2. Replace a dirty filterCheck the furnace air filter and replace it if it is clogged.
3. Open vents and return grillesMake sure supply registers and the return grille are not blocked.
4. Clear outdoor terminationsFrom the ground, look at the vent and combustion-air pipe ends and clear obvious snow or debris.
5. Try one restartSet the thermostat back to heat. If four flashes return, call a technician.

Frequently asked questions

Does four flashes mean the same thing on every Trane furnace?

Not necessarily. This definition comes from Trane's installer guide for the Integrated Furnace Control it covers. Check the wiring-diagram label on your furnace, and look up your model's literature at Trane's library.

Why does the blower keep running with four flashes?

Trane's table does not describe blower behavior for this code. Carrier's table for the equivalent code says the blower runs for four minutes or until the open switch closes; that is another brand's behavior, so do not assume it for Trane.

Sources

• Installer's Guide 18-CH49D1-1: SiNi Igniter Assembly IGN00117 (includes the Integrated Furnace Control error flash codes) (Trane) Covers: Trane and American Standard furnaces using the Integrated Furnace Control (IFC) covered by this installer guide (dated 04/09). Newer boards can differ; check the wiring-diagram label inside your furnace.
• SP05-59 Service and Maintenance Procedures: Deluxe 4-Way Multipoise 2-Stage Direct-Vent Condensing Gas Furnace (Carrier (shareddocs.com)) Covers: Carrier 2-stage condensing gas furnaces with the status-code LED control described in the document. Other Carrier, Bryant and Payne boards can use different codes; check the service label on your furnace.
• RS6612023 Service and Troubleshooting: 34.5" Chassis ACVC96/AMVC96/GCVC96/GMVC96 Gas Furnaces (Goodman Manufacturing (Daikin)) Covers: Goodman and Amana 96% two-stage condensing furnaces in the 34.5" chassis.

Safety note: this page is general information drawn from the sources above. Gas, combustion and line-voltage repairs belong to a licensed professional. Your own equipment's label and manual take priority over anything here. Read the full disclaimer.