What does a blinking red light mean on a Trane furnace?

A blinking red light on a Trane furnace can mean numerous things, depending on the speed of the blinking and the number of times that the light blinks. Continuous (slow or fast) flashing indicates that your furnace is on and either calling (fast) or not calling (slow) for heat. This is a normal part of your furnace's operation and is not a cause for concern.