My Trane XE80 will ingnite, shut off, ignite, shut off. Cleaned the flame sensor and still have problem that blower motor doesn't come on, but it sounds like it is trying to come on. Could this be the startup capacitor?

Also found the diagnostic light - which gives 4 blinks, indicating "Thermal Protection Device Open". What device could this be?

Would greatly appreciate help, as the temperature is down to 65F inside and below freezing outside.