Trane furnace blinking 8 times: low flame sense signal

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

What eight flashes mean

Trane's IFC error table in installer guide 18-CH49D1-1 lists 8 flashes: Low flame sense signal. It is distinct from 5 flashes (flame sensed when no flame should be present) and 9 flashes (check the ignitor circuit and the line N to 24 VAC common voltage, 2 volts or less, with a possible grounding problem).

How flame sensing works

Carrier's flame sensor guide explains the principle used in modern gas furnaces: the control passes a very small electrical current through the flame (flame rectification) and uses it to confirm combustion. If the control does not get the signal it expects, it can close the gas valve. Carrier lists carbon buildup or oxidation on the sensor rod, a cracked insulator, a bent or misaligned rod, loose wiring, poor grounding and age as reasons a sensor reads poorly.

Carrier's technician service document, for its own control, gives numbers: 0.5 microamps DC is the minimum flame-sense signal and 4.0 to 6.0 microamps is nominal. Trane's table does not give a number, so do not apply Carrier's values to a Trane control.

What to do about it

This is a service call. Carrier recommends that a trained HVAC professional maintain and clean internal parts like the flame sensor, and Trane's installer guide warns about label-before-disconnect wiring and an uninterrupted ground. A technician can measure the actual sensor signal, inspect the rod and ceramic, and check the grounding.

Frequently asked questions

What is the difference between 5 flashes and 8 flashes?

Five flashes means flame is sensed when none should be present. Eight flashes means the flame sense signal is low.

Will cleaning the flame sensor fix 8 flashes?

It can, because buildup is a common reason for a weak signal, according to Carrier. But Trane's table lists only the code, so a technician should confirm the cause, including grounding, before replacing parts.

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.
• Furnace Flame Sensor: What It Is, Why It Fails, and How to Fix It (Carrier)
• 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.

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.