Furnace starts and stops repeatedly without reaching the set temperature; thermostat clicks frequently.

Safety: Turn off power before working on thermostat wiring.

Steps:

• Check thermostat settings: For digital thermostats, set the cycle rate or heat cycles per hour according to Atlantic furnace recommendations (often 3–5 cph).
• Relocate thermostat: Ensure the thermostat is not near supply vents, exterior doors, or direct sunlight.
• Tighten connections: Remove the thermostat cover and tighten all terminal screws. Ensure no bare wires are touching.
• Test with jumper: Temporarily jumper R to W at the furnace to see if the furnace runs normally. If so, the thermostat may be faulty.

Note: Replace the thermostat if settings and wiring are correct but cycling persists.