Thermostat clicks or relays chatter rapidly when calling for heat or cool; equipment may short‑cycle.

Safety first: Turn off power to the furnace/air handler before working on wiring.

• Tighten connections: Secure all thermostat and control board terminal screws. Ensure good copper contact.
• Inspect transformer: Listen for buzzing or humming from the Payne transformer. If excessive, have it tested and replaced if necessary.
• Separate wiring: Ensure thermostat cable is not bundled tightly with high‑voltage wiring, which can induce noise.
• Replace thermostat: If chatter persists with solid wiring and good voltage, the thermostat's internal switching components may be failing and the unit should be replaced.