York TM9T100C16MP11 Error Code 5 Red Flashes: Limit Circuit Open Over 15 Minutes
What Does Code 5 Red Flashes Mean?
A 5 red flashes code on the York TM9T100C16MP11 is set when the limit circuit remains open for more than fifteen minutes. At that point the board stops assuming simple overheating and concludes that a manual-reset rollout switch has tripped. Rollout switches open when flames escape the burner box and roll outward — a condition tied to a blocked heat exchanger, poor combustion air, or restricted venting.
The furnace has entered a hard lockout and will not restart on its own. Power must be cycled off and on to reset the control, but only after the underlying problem is corrected. Simply resetting power without fixing the root cause is dangerous, because a rollout event can accompany a cracked heat exchanger that allows carbon monoxide into the home's air.
This is the most severe end of the limit-circuit escalation. It follows the 4 red flashes limit trip and is more serious than 11 red flashes, which indicates the limit stayed open only 5 to 15 minutes (a blower failure) rather than beyond 15 minutes.
What You'll Notice
- There is no heat and the furnace will not restart on its own (hard lockout).
- You may notice a hot, burnt, or scorched smell near the burner area.
- There may be visible soot or heat discoloration around the burner compartment.
- The board shows five red flashes.
- It may follow a period of repeated overheating or 4 red flash limit trips.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Manual-reset rollout switch has tripped | Most common | ✗ Call a pro → |
| Primary heat exchanger failure or burner problem | Common | ✗ Call a pro → |
How This Is Diagnosed
A technician inspects the primary heat exchanger for cracks, checks the combustion air supply and the venting for restriction, verifies the inducer is drawing properly, and examines the burners for signs of flame rollout. The rollout switch itself is tested. Only after the root cause is corrected does the technician manually reset the switch and cycle power to clear the lockout.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- The furnace is in hard lockout showing five red flashes and will not restart
- You see soot, scorching, or flames outside the burner compartment
- You are concerned about a cracked heat exchanger or carbon monoxide
- The code returns after power is cycled
Frequently Asked Questions
Can I just reset the furnace after 5 red flashes?
No. Resetting power without fixing the root cause is unsafe, because this code can accompany a cracked heat exchanger and carbon monoxide risk. A technician must find and correct the cause first.
Is a rollout switch trip dangerous?
Yes. It means combustion is escaping the burner box, which can produce carbon monoxide. Make sure your CO detectors are working and have the furnace inspected before running it.
How is 5 red flashes different from 4 and 11 red flashes?
All involve the limit circuit: 4 red flashes is the initial limit trip, 11 red flashes is a hard lockout after 5 to 15 minutes (blower failure), and 5 red flashes is a hard lockout after more than 15 minutes (rollout).
Sources
✓ Verified against manufacturer service manual — March 2026