A furnace that starts and stops every few minutes is called short cycling. It wastes gas, wears parts and leaves rooms unevenly heated.
Overheating from restricted airflow
A clogged filter, closed registers or blocked returns trap heat in the furnace until the high-limit switch shuts the burners off. Once it cools, it starts again. Replace the filter and open vents.
Dirty flame sensor
If the burners light and then go out after a few seconds, the flame sensor may not be proving the flame. The furnace retries, giving an on-off pattern.
Thermostat problems
A thermostat near a supply register, a lamp, a sunny window or the kitchen can satisfy itself quickly. Low batteries or loose wiring cause erratic cycling too.
An oversized furnace
A furnace too big for the house heats the air near the thermostat fast and shuts off before the rest of the house warms. Common when an old furnace was replaced with the same size after insulation or new windows were added.
Blocked venting or condensate problems
On high-efficiency furnaces, blocked PVC vents (snow, nests) or a clogged condensate drain can trip safety switches and cause cycling or lockouts.
Start with the filter and thermostat. If cycling continues, call (312) 924-7223 for furnace repair in Chicago.