Furnaces sometimes engage in short cycling, which is when the furnace cycles on and off for very short periods of time. This leads to major inefficiencies and also indicates that there is something wrong with the furnace. The continual cycling on and off can lead to damage in the starter equipment, which can shorten the lifespan of the furnace, since the cycling puts more strain on the starter components. The problem may be from a restricted air flow, which can come from a clogged furnace air filter.

Furnaces cycle on and off when they have a malfunction.

Dirty Ducts

The furnace owner might need to have the air ducts cleaned also. In some cases, the ducts might even have collapsed, preventing air from effectively flowing through the ducts. These ducts collapse under the weight of the debris.

Dampers and Registers Close

Closed balancing dampers and/or registers can cause the furnace to cycle on and off. The dampers and registers are the devices that regulate the flow of heat and air through the furnace system. When closed, they prevent adequate heat from entering into the spaces that need to be warmed up.

Thermostat Issues

Also, the furnace cycling could be the result of a poorly placed thermostat. To function properly, thermostats should be placed in the most commonly used room in the house. However, thermostats need to be away from drafts, windows and outside walls because these areas can have different temperatures than the rest of the home. The thermostat might also have a loose wire or other mechanical problem.


One of the worst conditions involves the furnace overheating. When the furnace gets too hot, the furnace cycles off to prevent damage. In this circumstance, the owner should definitely call a technician. Sometimes the heat exchanger has a crack that can lead to the furnace overheating. Dirty furnaces are one of the most common causes of overheating.

Igniters with Off Cycles

Some igniters have a lot of off cycles. This can cause property owners to have very high heating bills. Furnace owners should find out how many off cycles the igniter has before purchasing the furnace.

Poorly Sized Furnaces

Furnaces that are too large for the particular building will tend to cycle on and off. Properly sized furnaces should run continuously on cold days instead of cycling on and off. The contractor who installs the furnace should know when the furnace is the right size.

LED Warning

When the furnace cycles on and off, the furnace sometimes has a monitoring system that generates an LED light when there is something wrong with the furnace that indicates what the furnace problem is.