Error Code Slow Flash
Info

Trane TUH1B080A9H31A Error Code Slow Flash: Normal - No Call for Heat

TL;DR
Your furnace is in standby mode with no active call for heat — this is completely normal.
Disclaimer
This article is for informational purposes only and does not guarantee the accuracy or completeness of the information provided. Always turn off power and gas supply before attempting any repairs. If you smell gas, leave immediately and call your gas company. Consult a licensed HVAC technician for diagnosis and repair. Any actions taken based on this information are at your own risk.

What Does Code Slow Flash Mean?

A slow-flashing LED on the Trane TUH1B080A9H31A control board indicates the Integrated Furnace Control (IFC) is powered and functioning normally in standby mode. The thermostat is not currently requesting heat, so the furnace is idle and waiting. All self-diagnostic checks have passed with no faults detected.

If you expect the furnace to be running, check your thermostat settings. Confirm it is set to "Heat" mode and the target temperature is higher than the room's current temperature. Some programmable thermostats have schedules that may have lowered the setpoint, and dead batteries can cause a thermostat to lose its settings entirely.

This LED pattern requires no service or maintenance. It is the expected indication when the furnace is operating normally and no heating demand exists.

Contact a licensed HVAC technician if any of these apply:

Sources

  1. Installer's Guide - Upflow/Horizontal, Downflow/Horizontal, Gas-Fired, Direct Vent Condensing Furnaces

✓ Verified against manufacturer service manual — March 2026