Check whether the error appears on all thermostats. If so, check that the system's main control board is operating properly. To do so, check the behavior of all its self-diagnostic LED.

If the status of the main control board's LED is correct, check the thermostat's coverage with the main control board. To do so, bring the thermostat closer to the main control board and, if it re-establishes communication, it will be necessary to relocate the thermostat because it had no coverage.

If it is not recovered, check whether the battery is charged and operating properly. To do so, remove and reinsert the battery. If the Think screen is not refreshed, the battery has been used up and should be replaced.

If the Think screen is refreshed and displays Error 1 again, restart the zone and associate it to the system (How can I reset a zone equipped with a Think thermostat when it displays Error 1?).

If the problem is not solved, restart the entire system and reassociate it (How do I reset the entire system?).