York TM9T100C16MP11 Error Code 10 Red Flashes: Gas Valve Energized Without Call for Heat
What Does Code 10 Red Flashes Mean?
A 10 red flashes code on the York TM9T100C16MP11 means the board has detected that the gas valve is receiving power without a thermostat call for heat. The valve should only be energized during an active heating cycle, so the board treats this as a safety hazard: it runs the main blower and inducer to ventilate the furnace and refuses to start any ignition sequence while the condition exists.
The most common cause is a faulty gas valve with an internal short or stuck solenoid that draws power through an unintended path, or damaged gas-valve wiring that creates a circuit energizing the valve outside the board's normal command. In either case the valve could open when it should not, allowing gas to flow without controlled ignition.
It is important to tell this apart from the 1 red flash code. Ten red flashes means the gas valve is being electrically energized without a call for heat, while 1 red flash means the sensor actually detected a flame without a call for heat. Both are gas-safety codes, but they identify different failures.
What You'll Notice
- The blower and inducer run even though the thermostat is not calling for heat.
- No ignition sequence is attempted.
- The board shows ten red flashes.
- You may notice a gas odor if the valve is passing gas.
- The furnace will not return to normal standby.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Faulty gas valve | Most common | ✗ Call a pro → |
| Faulty gas valve wiring | Common | ✗ Call a pro → |
How This Is Diagnosed
A technician checks the gas valve coil and its wiring for a short or a stuck-energized condition, inspects the board's valve-drive circuit, and confirms the valve de-energizes and fully closes when it should. Because every likely cause involves the gas valve or its wiring, this is diagnosis and repair for a professional, not a homeowner task.
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 blowers run with no call for heat and the board shows ten red flashes
- You smell gas around the furnace
- The furnace will not return to its normal standby state
- The code persists after the furnace power is cycled
Frequently Asked Questions
What is the difference between 10 red flashes and 1 red flash?
Ten red flashes means the gas valve is being energized without a call for heat (an electrical fault), while 1 red flash means an actual flame was sensed without a call for heat.
Is it safe to keep running the furnace?
No. Turn the furnace off at the breaker and call a technician. If you smell gas, leave immediately and call your gas company from outside.
Can I fix a 10 red flashes code myself?
No. Gas valve and gas-valve wiring diagnosis is a safety-critical job for a qualified technician.
Sources
✓ Verified against manufacturer service manual — March 2026