York TM9T100C16MP11 Error Code 8 Red Flashes: Flame Lost Five Times (Recycle)
What Does Code 8 Red Flashes Mean?
An 8 red flashes code on the York TM9T100C16MP11 means the flame was lost five times (four recycles) during a single heating cycle. The furnace ignited each time, but the flame kept dropping out, and after exhausting its retries the board entered a one-hour soft lockout.
The most common cause is a dirty flame sensor. The sensor conducts a tiny current through the flame to confirm it is lit; as carbon and oxidation build on the rod, the signal weakens until the board can no longer reliably detect flame and closes the gas valve. Low gas pressure can also cause repeated dropouts if the flame is too weak or unsteady, and a faulty gas valve that does not open fully is a less common possibility.
This code often follows the continuous amber flash, which is the earlier warning that flame-sense current has dropped below 1.5 microamps — the 8 red flashes lockout is where that weakening signal ends up. It is distinct from the 7 red flashes code, where the flame never establishes at all.
What You'll Notice
- The burner lights, then the flame goes out, relights, and repeats.
- The furnace short-cycles several times, then locks out for about an hour.
- The board shows eight red flashes.
- The condition may have been preceded by a continuous amber (low flame current) warning.
- Heat output is intermittent and unreliable.
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 → |
How This Is Diagnosed
A technician cleans or replaces the flame sensor, then measures the flame current at the board's flame-current test pad to confirm it exceeds 1.5 microamps. If the current is still marginal with a clean sensor, the gas pressure is checked and the gas valve and burner are inspected. Because verifying the repair on this model relies on measuring the microamp flame current, it is handled as a professional check rather than a do-it-yourself fix.
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 lights but the flame keeps going out and it locks out with eight red flashes
- You previously saw a continuous amber (low flame current) warning
- The problem continues after the flame sensor is cleaned
- The burner flame looks yellow or unsteady rather than a crisp blue
Frequently Asked Questions
What is the difference between 8 red flashes and 7 red flashes?
Eight red flashes means the flame lit but was lost five times during the cycle, while seven red flashes means the flame never established across three ignition trials.
Is it just a dirty flame sensor?
Often, yes, but on this model confirming the fix requires measuring the flame current above 1.5 microamps and ruling out low gas pressure or a faulty gas valve, so a technician should verify it.
How does this relate to the continuous amber flash?
The continuous amber flash is the early warning that flame-sense current is low. If it keeps dropping and the flame is lost repeatedly, the board escalates to the 8 red flashes lockout.
Sources
✓ Verified against manufacturer service manual — March 2026