Furnace short cycles

The furnace runs briefly and shuts down before satisfying the thermostat, then restarts.

Heating

normal

Possible cause

Limit and Rollout Switches
Component
Temperature safeties that shut down heating equipment, and what each one is actually reporting.

Affected equipment

Gas Furnace
Equipment
How a modern forced air gas furnace proves each condition before it allows the next step.

Background

Airflow Fundamentals
Concept
CFM, static pressure and why airflow problems are behind a large share of service calls.
Flame Sensing and Rectification
Concept
How a furnace proves flame with a single rod, and how to measure and interpret the microamp signal.

Local Code Notice

HVAC installation, venting, combustion air, ventilation air, gas piping, clearances, termination locations, electrical requirements, permits, and equipment requirements vary by jurisdiction and equipment. Always verify the applicable local codes, adopted code edition, regulations, permits, and manufacturer installation instructions before installation or service.