York TM9T100C16MP11 Error Code 5 Red Flashes: Limit Circuit Open Over 15 Minutes
What Does Code 5 Red Flashes Mean?
A 5 red flash code on the York TM9T100C16MP11 indicates the limit circuit has remained open for more than fifteen minutes. When the limit stays open this long, the control board assumes a manual-reset rollout switch has tripped rather than a simple overheating event. Rollout switches trip when flames escape the heat exchanger and "roll out" toward other components — a condition that often signals a cracked or failed heat exchanger.
The furnace has entered a hard lockout, meaning it will not attempt to restart on its own. Power must be cycled off and back on to reset the control after the underlying problem has been corrected. Simply resetting power without fixing the root cause is dangerous, as the rollout switch tripped for a safety reason.
A qualified HVAC technician must inspect the combustion chamber, check for proper combustion air supply, verify inducer motor operation, and examine the primary heat exchanger for cracks or failure. A cracked heat exchanger can allow carbon monoxide to enter your home's air supply, making this a high-priority safety repair.
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 → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Immediately — this code often indicates a heat exchanger failure or combustion safety issue that poses a carbon monoxide risk
Sources
✓ Verified against manufacturer service manual — March 2026