York TM9T100C16MP11 Error Code 8 Red Flashes: Flame Lost Five Times (Recycle)
What Does Code 8 Red Flashes Mean?
The 8 red flashes code on the York TM9T100C16MP11 indicates the flame was lost five times (four recycles) during a heating cycle. The furnace successfully ignited each time but the flame kept going out during operation. After exhausting its retry attempts, the system entered a one-hour soft lockout.
The most common cause is a dirty flame sensor. The flame sensor is a thin metal rod that conducts a tiny electrical current through the burner flame to confirm it is lit. Over time, carbon deposits and oxidation build up on the rod, weakening the signal until the control board can no longer reliably detect the flame and shuts off the gas valve.
Low gas pressure can also cause this code. If the gas supply is inadequate, the flame may be too weak or unsteady for the sensor to detect consistently. A faulty gas valve that does not open fully is another less common possibility.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Dirty flame sensor | Most common | ✗ Call a pro → |
| Low gas pressure | Common | ✗ Call a pro → |
| Faulty gas valve | Uncommon | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The flame sensor still causes flame loss after thorough cleaning
- The flame ignites but goes out within seconds every time
- You notice the flame color is yellow or orange instead of blue
- The sensor rod is visibly pitted or corroded beyond what cleaning can restore
- You suspect a gas pressure issue (weak or flickering flame)
Sources
✓ Verified against manufacturer service manual — March 2026