TRANE Furnace XE 90, model TUX100C960C1 The heating cycle starts with forced air pump starting, working for several minutes, then a relay clicks, the pump stops, immediately restarts and again works for several minutes, this sequence repeats several times, then the burner ignites, works normally as necessary to warm the house, then stops normally. In the past, the burner was starting after the forced air pump started and worked for several seconds.