Hitachi controls-thermostats — ATW-RTU room thermostats paired with ATW-IOT-01 on Yutaki systems Error Codes Directory

Hitachi Yutaki alarms 77 and 78: the radio link, not the heat pump

Both alarms are about communication rather than heating. Alarm 77 means the Yutaki unit has lost communication with the ATW-IOT-01 interface, and alarm 78 means communication between ATW-IOT-01 and the ATW-RTU-12 thermostat has failed. Applies to: ATW-RTU room thermostats paired with ATW-IOT-01 on Yutaki systems These alarm numbers belong to the ATW-RTU room thermostat and the ATW-IOT-01 interface on Yutaki systems, as published in the Hitachi installation and operation manual for those controls. Yutaki units raise their own alarms in their own numbering, and a number seen on a wired controller is not necessarily the same number seen on the room thermostat. Owner-safe checks: Record the alarm exactly, including any decimal, and note which display you read it on. | Confirm the ATW-IOT-01 interface is powered, which is the first check the manual lists for both alarms. | Note whether anything changed in the property recently, such as a new appliance, a partition, or a repositioned thermostat. Qualified technician: Wiring integrity, wire loops, and interference sources on the Yutaki to interface link are installer work rather than owner checks. | A repeating alarm 78.1 is assigned to the room thermostat hardware and the manufacturer response is replacement, which should be arranged rather than attempted.