Thermal protection device open indicator light blinking on a Trane gas furnace how do I fix it.

Probably high limit safety. Look for a small, usually black square screwed to the plenum. Will have 2 wires. Remove wires, test with an ohmmeter, should read zero. You can do a quick test by connecting a jumper across the disconnected wires and see if the furnace fires off. If it does, DO NOT run the furnace, get a replacement first. These usually shut off when the plenum temperature is too high due to reduced airflow. Check ductwork and filters.

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