Will not light or cuts out: usually the ignition system, a flame sensor coated in dust, an overheating trip from a blocked filter or return air, or a pressure switch fault. Cold air from the vents: the burner is not lighting or not staying lit, so the fan is just moving roof-space air. Error codes: each brand has its own, pointing to ignition, overheating, airflow or the control board. Noise: worn fan bearings, a loose panel or a failing motor. Weak airflow to some rooms: often not the heater at all, but a disconnected or crushed duct, which our duct repair service fixes.