Thermostat frequently reboots or restarts, especially when heating or cooling equipment turns on.

Safety: Turn off power to HVAC equipment before inspecting wiring.

• Step 1 – Inspect connections: Tighten all low‑voltage terminal screws at the thermostat and furnace/air handler control board, especially R and C.
• Step 2 – Check transformer rating: Verify the VA rating of the 24 VAC transformer is adequate for the thermostat plus any connected accessories (humidifier, zone dampers, etc.).
• Step 3 – Measure voltage under load: With equipment running, measure voltage between R and C at the thermostat. If it drops significantly below 22 VAC during operation, the transformer may be undersized or failing.
• Step 4 – Offload accessories: Power high‑draw accessories from a separate transformer instead of through the thermostat if possible.
• Step 5 – Replace transformer or thermostat: Replace the 24 VAC transformer if it cannot maintain voltage. If voltage is stable but reboots continue, the thermostat’s internal power supply may be defective; replace the thermostat.