Thermostat backlight flickers or display brightness changes unexpectedly.

Safety first: Turn off power to the furnace/air handler before reseating the thermostat.

• Reseat thermostat: Remove the thermostat from its wall plate and snap it back on firmly to ensure good pin contact.
• Tighten R and C terminals: Secure low‑voltage connections at the thermostat and control board.
• Measure voltage (advanced): Check for stable 24VAC at the thermostat under load. If it fluctuates, have the transformer or wiring inspected.
• Replace thermostat: If voltage is stable but flicker persists, the internal display driver is likely failing and the thermostat should be replaced.