York TM9T100C16MP11 Error Code Slow Amber Flash: Normal Operation - Call for Heat
What Does Code Slow Amber Flash Mean?
On the York TM9T100C16MP11 control board, a slow amber flash — about two seconds on and two seconds off — confirms the furnace has received a call for heat from the thermostat and is carrying out a normal heating cycle. York built this as a two-stage furnace, so during this indication the unit may be running on low or high fire depending on how much heat the space needs.
This is the active-operation counterpart to the slow green standby flash. When the thermostat is satisfied and the cycle ends, the board returns to a slow green flash. During a normal cycle you should hear the inducer start first, then igniter warmup, the gas valve click, and burner ignition, with the main blower starting after a short delay to let the heat exchanger warm up.
Do not confuse this normal slow amber flash with the continuous amber flash, which is a distinct warning that the flame-sense current has dropped below 1.5 microamps. The slow amber is a steady two-second rhythm; the continuous amber flickers quickly with no long pauses. If the board ever switches from slow amber to a red flash count, that number identifies a specific fault.
What You'll Notice
- The LED blinks amber with a slow, steady rhythm of about two seconds on and two seconds off while the furnace runs.
- Warm air is delivered from the registers and the inducer, burners, and blower operate normally.
How This Is Diagnosed
No diagnosis is needed — this is the normal operating indication. To confirm it is behaving correctly, verify that warm air reaches the registers while the amber flash is active and that the board returns to a slow green flash once the thermostat is satisfied. If the board switches from slow amber to a red flash count without producing heat, note the number of flashes and look up that specific fault code.
- The slow amber flash is showing but no warm air is being delivered to the living spaces
- The furnace runs continuously and never returns to the slow green standby flash after the space has warmed up
Frequently Asked Questions
What does a slow amber flash mean on my York TM9T?
It means the furnace is operating normally and is actively responding to a call for heat. No action is required.
Should I be worried about a slow amber flash?
No. It is a normal indication of a healthy heating cycle. Only red flash codes indicate a fault on this control board.
What is the difference between the slow amber and continuous amber flash?
The slow amber flash is normal operation with a call for heat, while the continuous amber flash (a fast flicker with no long pauses) is a warning that the flame-sense current has fallen below 1.5 microamps.
Sources
✓ Verified against manufacturer service manual — March 2026