Error Code Slow Amber Flash
Info

York TM9T100C16MP11 Error Code Slow Amber Flash: Normal Operation - Call for Heat

TL;DR
Your furnace is actively responding to a thermostat call for heat — normal operation.
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 Amber Flash Mean?

A slow-flashing amber LED on the York TM9T100C16MP11 control board indicates the thermostat is calling for heat and the furnace is running through its heating sequence. The two-stage furnace is either in the startup process or actively heating your home. This is completely normal.

During a typical heating cycle, you should hear the inducer motor start first, followed by igniter warmup, the gas valve click, and burner ignition. The main blower starts after a short delay to allow the heat exchanger to warm up. On this two-stage furnace, the system may operate at low fire or high fire depending on heating demand.

If the furnace does not seem to be producing heat despite this amber flash, the startup sequence may be encountering a problem that has not yet triggered a fault code. Monitor the LED for any change to a red flash pattern, which would indicate a specific fault condition.

Contact a licensed HVAC technician if any of these apply:

Sources

  1. Installation Manual - Residential Gas Furnace Models TM9T*MP (96% AFUE Two Stage Multi-position)

✓ Verified against manufacturer service manual — March 2026