York TM9T100C16MP11 Error Code 7 Red Flashes: Ignition Failure - No Flame Detected

What Does Code 7 Red Flashes Mean?

A 7 red flashes code on the York TM9T100C16MP11 means the flame could not be established during three trials for ignition. After the third failure the furnace enters a one-hour soft lockout and will automatically try again when the hour ends. During each trial the hot surface igniter heats up, the gas valve opens, and the board looks for a flame signal; if none appears, the valve closes and it retries.

The most common cause is a faulty or cracked hot surface igniter that no longer reaches ignition temperature — that is a professional replacement, not a homeowner repair. There are, however, two homeowner-safe checks: the gas valve switch may simply have been left in the OFF position (for example after service), and a dirty flame sensor can prevent the board from confirming the flame. Low or no gas pressure, a faulty gas valve, loose wiring, or a burner problem are other causes that require a technician.

This code is distinct from the 8 red flashes code. A 7 red flashes means the flame never established across three trials, while 8 red flashes means the flame did light but was then lost five times during the cycle.

What You'll Notice

• The furnace attempts to start, clicks or cycles, then goes quiet with no heat.
• The igniter may glow but the burner never lights, or the igniter does not glow at all.
• The board shows seven red flashes and the furnace locks out for about an hour before retrying.
• You may hear the gas valve click without a sustained flame following.
• Repeated failed start attempts, then no further attempts during the lockout.

Common Causes

How to Fix It: Check the Gas Valve Switch and Clean the Flame Sensor

What You'll Need

• 1/4-inch hex head driver or nut driver
• Scotch-Brite pad
• Flashlight

Steps

1. Turn off electrical power at the breaker and shut off the gas supply valve Locate the furnace circuit breaker and flip it to OFF. Turn the gas shutoff valve to the OFF position (perpendicular to the pipe). If you smell gas, leave immediately and call your gas company from outside.
2. Check the gas valve switch position Locate the gas valve on the furnace and confirm its ON/OFF switch is in the ON position. If it was left OFF after service or a gas interruption, this alone can cause the ignition failure.
3. Locate the flame sensor Open the furnace access panel and look near the burner assembly. The flame sensor is a thin metal rod, usually bent at an angle, mounted with a white porcelain insulator and a single wire, secured by one mounting screw.
4. Remove the flame sensor Disconnect the wire from the flame sensor, remove the mounting screw, and carefully pull the sensor out. Handle it by the porcelain insulator or bracket, not the metal rod.
5. Clean the sensor rod Gently clean the flame sensor rod with a Scotch-Brite pad until the metal is dull-bright. York's guide lists fine steel wool as the cleaning material, but many HVAC technicians prefer a Scotch-Brite pad because it leaves no abrasive residue on the rod. Do not clean or scratch the white porcelain base, and take care not to bend the rod.
6. Reinstall the flame sensor Place the sensor back in its bracket, secure the mounting screw, and reconnect the wire so the rod will sit in the flame path when the burners ignite.
7. Restore power and gas, then test Turn the gas supply valve to ON and flip the breaker to ON. Cycling the power also clears the lockout. Set the thermostat to call for heat and watch the ignition sequence.

When to Call a Professional

Contact a licensed HVAC technician if:

• The igniter does not glow at all during the ignition sequence
• The gas valve switch was already ON and the code returns after cleaning the flame sensor
• You can hear gas but it does not ignite
• The flame lights but goes out within seconds
• You smell gas near the furnace

✓ Verified against manufacturer service manual — March 2026