Thermostat displays A6 and cannot pair with the Viessmann gateway or boiler interface; local app control fails.

Safety first: Only handle low‑voltage devices and follow manufacturer instructions. Do not open sealed electronic modules.

• Reset pairing: Put the thermostat into pairing mode as described in the manual (often via a menu option or button combination). Ensure the gateway is also in pairing mode.
• Reduce interference: Temporarily turn off or move away cordless phones, baby monitors, or other 2.4 GHz devices that may interfere.
• Check distance: Place the thermostat and gateway within a few meters of each other during pairing.
• Update firmware: Use the Viessmann app to check for firmware updates for the gateway and thermostat. Apply updates and retry pairing.
• Factory reset if needed: As a last resort, perform a factory reset on the thermostat and re‑add it to the system, then reconfigure schedules.