A faulty thermostat can cause short cycling. Check to be sure the season setting is correct. Check the filter and replace it if it’s clogged with dust and debris. When the exchanger heats up to the maximum temperature, the furnace shuts off after a few minutes it may be caused by restricted air flow. The furnace is designed to pull filtered air into the blower, if the filter matted with dust, pet hair or other debris the system strains to perform this critical function. Open all of air supply vents to the systems they are designed to circulate the total air mass for all areas, a closed vent is considered a restriction in the system.