York TM9T100C16MP11 Error Code 2 Red Flashes: Pressure Switch Stuck Closed
What Does Code 2 Red Flashes Mean?
Before it energizes the inducer, the York TM9T100C16MP11 verifies that the pressure switch contacts are open. This proves the switch has not been jumpered or stuck closed and can be trusted to confirm draft later in the cycle. A 2 red flash code means the board found the contacts already closed at the beginning of the heat cycle, so it refuses to continue the ignition sequence.
The most common cause is a faulty pressure switch whose internal contacts have stuck together. A miswired switch — for example after recent service or a parts swap — can also present as closed when it should be open.
This is a start-of-cycle self-check and is distinct from the other pressure-switch codes on this board. The 3 red flashes code means the switch is open when it should be closed (no proven draft after the inducer runs), and the 6 red flashes code means the switch closed normally but then opened repeatedly during operation. Describing which of the three is present helps a technician target the fault.
What You'll Notice
- The furnace never starts its ignition sequence and shows two red flashes.
- The inducer may not start, or the startup stalls immediately.
- There is no heat despite repeated attempts to call for it.
- The code often follows recent service or a pressure-switch replacement.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Faulty pressure switch stuck in closed position | Most common | ✗ Call a pro → |
| Miswiring of pressure switch | Common | ✗ Call a pro → |
How This Is Diagnosed
A technician tests the pressure switch with a meter at rest, where the contacts should read open; if they read closed, the switch is stuck and is replaced. The wiring is inspected for a short or an incorrect connection that could hold the circuit closed, and the correct switch part number and pressure rating are confirmed. The switch is never bypassed, because it is a critical venting safety device.
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 will not begin its ignition sequence and shows two red flashes
- The code appeared right after recent service or a parts replacement (possible miswiring)
- The code persists after the furnace power is cycled
Frequently Asked Questions
What does 'pressure switch stuck closed' mean on a York TM9T?
It means the switch contacts are closed before the inducer has created any draft. The board treats this as a failed safety self-check and will not allow ignition.
What is the difference between 2 red flashes and 3 red flashes?
Two red flashes means the switch is closed when it should be open at the start of a cycle, while three red flashes means the switch is open when it should be closed after the inducer runs.
Can I fix a stuck pressure switch myself?
No. Testing and replacing the pressure switch, and confirming its wiring, is a technician's job — the switch should never be bypassed.
Sources
✓ Verified against manufacturer service manual — March 2026