Your heater/furnace can develop issues for various reasons, including: Dirty air filters Improper thermostat settings A yellow pilot light Worn out mechanical components Strange noises Blower cycling Old age Need for frequent repairs While dirty air filters and wrong thermostat settings are simple fixes, strange noises, a yellow light, blower cycling, and worn out mechanical components need to be repaired by a professional. If your heater is over 15 years old, requires frequent repairs, and has multiple problems, it's time to invest in a new unit. The best way to stave off heater problems is to schedule routine maintenance.