A furnace that turns on and then shortly turns off before completing a heat cycle is a problem known as short cycling. Short cycling is a sign or a symptom of a problem. Depending on the cause, some short cycling problems can be easily corrected, while others will require the assistance of an HVAC technician. Hal Mechanical will share the different reasons why a furnace will short cycle.
Air Filters are Dirty
When your furnace first begins to short cycle, start by checking the air filters. Dirty air filters cause the furnace to work harder and more often. The longer and more frequent heating cycles cause the furnace to overheat. Therefore, to prevent serious damage or even a fire, the furnace’s safety system will turn the furnace off. A simple problem such as dirty air filters can cause a major thing such as short cycling. When the furnace first starts to short cycle, turn off the furnace to allow it to cool down and change out the air filters. Once the furnace has had time to cool down, start it back up and see if the short cycling problem has been corrected.
Obstructed Furnace Flue
A furnace that burns gas, oil, or propane will produce emissions or gases that are toxic. One of the common toxic gases produced in a furnace is carbon monoxide. All of the dangerous gases are safely ventilated outside through a flue. The flue rarely develops any problems. However, occasionally the flue can become blocked or obstructed. The flue can become blocked by bird nests, animals and debris. When the flue is blocked, the furnace’s flue limiter can detect the gases building up and turn off the furnace. Each time the furnace tries to run a cycle, the limiter will detect gas and turn off the furnace until the gases dissipate. Unless the flue gets cleaned out, the gases will never properly ventilate.
Furnace Flame Sensor Problems
Another component that can cause short cycling problems is the flame sensor. A flame sensor is another part of a furnace’s safety system. The flame sensor is designed to detect the flame from the pilot light. If the flame isn’t burning the flame’s sensor will prevent the furnace from starting up. If the pilot light flame goes out, gas will leak and lead to a fire. The flame sensor is designed to prevent this type of scenario. If the flame sensor is dirty or develops a problem, it will not think there is a flame. A flamer sensor often needs to be cleaned and eventually replaced during the life time of a furnace.
Hot Surface Igniter Problems
A modern furnace unit uses a hot surface igniter to ignite the gas and heat up the burners. If the hot surface igniter isn’t working properly or is damaged, then the furnace will not make it past the startup process. To determine if the hot surface igniter needs to be replaced, you will need a licensed HVAC technician to come and inspect the starter system.