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Hoymiles microinverter alarm and event codes — grid, protection and DTU faults — explained, with what each points to and what to check.
Hoymiles microinverters report faults as numbered alarm/event codes that surface in the S-Miles Cloud platform (and the S-Miles installer/end-user app) via the DTU gateway, and in the official user-manual "Troubleshooting List". The codes below are drawn from Hoymiles' own user manuals (HMT-1800, HM-800/700/600/500, HM-1200NT series) and from the community-decoded OpenDTU alarm table, which mirrors the codes Hoymiles' own DTU reports. Codes in the 120-149 band are the documented manual/grid-protection entries; lower numbers (11-73) are grid-disturbance warnings and protective-function events. Most accidental alarms self-clear once grid conditions return to normal; persistent or repeating alarms warrant contacting your installer or Hoymiles support.
30 of 30 codes
Warning: a sudden surge (spike) in grid voltage was detected. A grid-disturbance event rather than an inverter hardware fault.
Warning: a sudden sharp drop (sag) in grid voltage was detected.
Warning: an abrupt change (mutation) in grid frequency was detected.
Warning: an abrupt change in grid phase was detected.
Protection trip on the inverter (INV) stage due to overvoltage or overcurrent.
Overvoltage detected on the flyback (FB) transformer stage of the microinverter.
Overcurrent detected on the flyback (FB) transformer stage.
Overvoltage detected on the flyback clamp circuit.
Overvoltage detected on the flyback clamp circuit (second clamp channel).
Volt-Watt response active: the microinverter is reducing output power because grid voltage is high. Normal grid-support behaviour, not a fault.
Frequency-Watt response active: the microinverter is reducing output power because grid frequency is high. Normal grid-support behaviour.
Temperature-Watt derating active: the microinverter is reducing output power due to high temperature (around/above 80 C).
What to do
Improve ventilation and reduce ambient temperature at the install location; output recovers as temperature falls.
The microinverter has shut down on over-temperature protection because internal/ambient temperature exceeded safe limits.
What to do
Check ventilation and ambient temperature at the install position; if poor, improve heat dissipation/airflow. If conditions are within spec, contact your dealer or Hoymiles technical support.
The microinverter was shut down by a remote command (e.g. from the monitoring platform or DTU).
The grid profile / grid configuration parameters loaded on the microinverter are incorrect or invalid.
What to do
Verify the grid configuration parameter is correct and re-send/upgrade it. If the fault continues, contact your dealer or Hoymiles technical support.
Internal software/firmware error reported by the microinverter. Often transient.
What to do
If it occurs occasionally and the unit still works normally, no action is needed. If it recurs frequently and cannot recover, contact your dealer or Hoymiles technical support.
A firmware error was detected on the microinverter, typically related to a firmware version or failed upgrade.
What to do
Confirm the correct firmware version and re-run the upgrade; verify DTU-to-monitoring-system and DTU-to-microinverter communication. Contact your dealer if unresolved.
Internal software/firmware error reported by the microinverter. Often transient.
What to do
If occasional and the unit still works, no action needed. If recurring, contact your dealer or Hoymiles technical support.
Internal software error. Official Hoymiles manuals list it as "Software error code 129"; the OpenDTU decode labels the same code "Abnormal bias".
What to do
If occasional and the unit still works normally, no action needed. If it recurs frequently, contact your dealer or Hoymiles technical support.
The microinverter is offline — the DTU cannot communicate with it / it is not reporting to the monitoring system.
What to do
Check communication between the DTU and the Hoymiles monitoring system (and between DTU and microinverter); improve signal/connection if poor. Contact your dealer if it persists.
AC grid voltage exceeded the upper protection limit, so the microinverter stopped feeding in.
What to do
If accidental, the grid voltage was likely temporarily abnormal and the unit recovers automatically once voltage normalises. If frequent, monitor the grid voltage range and contact the local power operator.
The 10-minute average grid voltage exceeded the allowed limit (sustained overvoltage protection).
What to do
Usually recovers automatically once the averaged grid voltage returns within range; if persistent, contact the local power operator.
AC grid voltage fell below the lower protection limit.
What to do
Check that grid voltage is within the acceptable range; recovers automatically once normal. If it persists, contact the local power operator.
AC grid frequency exceeded the upper protection limit.
What to do
If accidental, the frequency was temporarily abnormal and the unit recovers automatically once it normalises. If frequent, contact the local power operator.
AC grid frequency fell below the lower protection limit.
What to do
Verify grid frequency is within range; recovers automatically once normal. Contact the local power operator if it occurs frequently.
The rate of change of grid frequency (ROCOF) exceeded the allowed limit.
What to do
Verify the frequency change rate is within the acceptable range; contact the power operator if it recurs.
A grid (utility) outage was detected; the microinverter cannot export with no grid present.
The microinverter detected disconnection from the grid (loss of AC connection).
What to do
Check whether there is a grid outage and verify the AC switch and wiring status.
Anti-islanding protection tripped — the microinverter detected an islanding condition and disconnected for safety.
What to do
Check whether there is a power grid outage and verify the AC switch/wiring status; the unit recovers when a stable grid is restored.
Anti-theft alarm — the system flags that a microinverter may have been removed/stolen.
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