Thermostat: Thermostat problems are the most common reason causing your furnace to not provide enough warmth. When the outside temperature is cold, do you find that you need to continually bump up your thermostat set point? After adjusting your thermostat upward does your system not turn your furnace on? You may be looking at a faulty thermostat.
If your thermostat is an older mechanical type, it may need to be recalibrated or leveled. If the thermostat was a DIY install by the homeowner, then it could be a wiring issue. When doing a thermostat repair, it is best to call a professional.
Furnace Filter: Another common issue is that the furnace may be shutting off early because it is overheating. This can be caused by a clogged furnace filter, a return air duct that is covered or blocked or too many of the warm air vents are shut or turned off. This limited airflow can cause your furnace to overheat.
Blocked Air Ducts: Over the years your system’s ducting may become clogged with dirt, lint and debris which can impede airflow and slow down the flow of warm air throughout your home. You should have air duct cleaning every 2-5 years as part of your system maintenance.
Not one of these issues? You will want to hire a reputable professional company to diagnose and repair your system!