Trane Furnace 3 Red Flashes bejo 6909 Share Trane Furnace 3 Red Flashes Web3 red flashes is a pressure switch error. Most likely a plugged condensate, or even just the port to the pressure switch is plugged. Is the vent motor coming in? Read also: 15 Best Female Monologues from Published Plays: Stand Out at Your Next Audition