Furnace short cycles (starts and stops frequently) without reaching set temperature

Safety: Turn off power before inspecting internal components.

• Check air filters and grilles: Ensure any return air filters, supply grilles, or hydronic convectors are clean and not blocked.
• Thermostat location: Make sure the thermostat is not located near a heat source, in direct sunlight, or above a radiator, which can cause premature shutoff.
• Observe furnace: Note whether the burner shuts off due to overheat (fan continues) or due to thermostat (furnace stops when room is still cold). This helps a technician diagnose.
• Professional assessment: If short cycling persists, a heating professional should check sizing, overheat controls, and system design.