HeatingCodesHow to read your furnace blinking light code
Step 1: Find the light
On Carrier's 2-stage condensing furnaces, the control's LED can be viewed through the sight glass in the blower door, and the service label is on the back of the main furnace door. Carrier's service document warns that removing the blower door cuts 115-volt power to the control, so the light only shows while the door is on and the furnace is powered.
Trane describes an LED on its Integrated Furnace Control, and Goodman describes a diagnostic LED or 7-segment display that shows a code. If you cannot see any light, check that the blower door is installed correctly and the furnace power switch is on.
Step 2: Count the flashes correctly
| Brand and control | How the code is counted | Example |
|---|---|---|
| Carrier (SP05-59 control) | Two digits: short flashes first, then long flashes | Three short + three long = code 33 |
| Trane / American Standard (IFC) | Count the flashes between pauses; slow flash and fast flash are normal states, not faults | 4 flashes = open temperature limit circuit |
| Goodman (96% two-stage) | Code shown on the control display or LED; see the service label and manual | Lockout resets after one hour or by interrupting power |
A steady light means something different from a code. On Carrier's control, continuous off means no 115 VAC at the control or no 24 VAC at the transformer, continuous on means the control has power, and rapid flashing means the 115 VAC polarity is reversed. On Trane's IFC, a slow flash is normal with no call for heat and a fast flash is normal during a call for heat.
Step 3: Look the code up for your brand
We only publish codes we could confirm in a manufacturer document, and each table says exactly which models the document covers. If your furnace is not covered, use the service label and manual for your model number instead of guessing from another brand.
Step 4: Do the low-risk checks first
Goodman's manual says improper filter maintenance is the most common cause of inadequate heating or cooling performance, and that filters should be cleaned or replaced about every two months or as required. So the first homeowner action for almost any code is the same: turn the thermostat off, replace a clogged filter, open the vents and look at the outdoor vent and intake terminations for snow or debris.
Lockouts and resets
A lockout means the control has stopped trying. Goodman describes lockout as three failed ignition attempts in one call for heat; the control resets itself after a one-hour lockout, and it can also be reset by interrupting 115-volt power or by lowering the thermostat so there is no call for heat for a short time. Carrier lists 3-hour auto-resets for its limit and ignition lockouts (codes 13 and 14). If a lockout repeats, stop resetting it and call a technician.
How to read a furnace blinking light code
- Find the LEDLook through the sight glass in the blower door or check the control board, with the blower door in place so the control has power.
- Count short and long flashesWatch several cycles. Note whether your brand counts short and long flashes separately (Carrier) or counts total flashes between pauses (Trane).
- Look up the code for your brandUse the code table for your furnace brand and confirm it matches the model covered by the manufacturer document.
- Do the safe checksReplace a dirty filter, open vents, and check the outdoor vent ends for snow or debris.
- Call a technician if it repeatsDo not keep resetting a lockout.
Frequently asked questions
Why does the same number of flashes mean different things on different furnaces?
Each manufacturer defines its own control board codes. Carrier code 33 is a limit circuit fault and Trane four flashes is an open temperature limit, but a furnace from another maker may use the same count for something else.
Can I reset a furnace lockout?
Several manufacturers allow resets by interrupting power or letting the control auto-reset (one hour in Goodman's manual, three hours for Carrier codes 13 and 14). Repeated lockouts point to a real fault and need service.
Sources
- 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.
- 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.
- 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.