Need help identifying your UPS alarm code?

As part of the building management systems and IT rooms, your Riello UPS will Identify and raise an alarm to notify you, if and when something is wrong.

However identifying whether your UPS requires immediate repairs can be difficult and trying to locate the service records or user manual is not always easy.

Riello units have sophisticated self-diagnostic system, the UPS can check and indicate on the display its status and any errors and/or faults that have occurred during its operation. When a problem arises, the UPS signals the event by showing the code and corresponding type of alarm on the display*.

*Different products may have a different set of alarms, but generally, the below applies to all.

S = Statuses

  • These codes indicate the current UPS status
  • No user operation is required, this just tells what’s going on
  • Example: S04 Load on Bypass (UPS is operating on bypass)

C = Commands

  • These codes indicate that a command has been activated
  • Shows what commands user has activated
  • Example: C08 Bypass Command Active (User has commanded UPS to transfer to bypass via HMI)

W = Warning

  • Messages that refer to a specific configuration or operation of the UPS
  • These show that there is a condition that may impact the operation of the UPS if not corrected
  • Example: W01 Battery Low Warning (UPS is operating from batteries and the autonomy is coming to an end shortly)

A = Anomalies

  • Minor problems that do not stop the operation of the UPS, but affect its performance or inhibit the use of some of its functions
  • Example: A05 Mains Overvoltage L1 (overvoltage on phase 1 on the input side)

F = Faults

  • Faults are problems more critical than “Anomalies” in that, if they persist, they may bring the UPS to a stop
  • Example: F23 Output Overload (Loading has exceeded UPS power rating and UPS is on overload)

L = Locks,

  • Locks indicate a breakdown of the UPS or one of its parts
  • Locks are normally preceded by an alarm signal
  • In the event of a fault and resultant breakdown of the inverter, the inverter will be switched off and the load will be powered by the bypass line (this procedure is excluded for breakdowns caused by high and persistent overloads and by short circuits)
  • Example: L26 Output Short-circuit L1 (UPS has detected an output low impedance fault in the Phase 1 and has prevented the use of inverter until fault has been cleared)

Below we have provided some of the more common alarm codes for your information:

Alarm Code





Load powered from bypass line



Battery operation



UPS locked: load not powered



UPS locked: load powered by bypass line



BOOST stage or battery charger locked – load not powered



Manual bypass active



Command active to power the load by the bypass line (from the panel)



End of discharge pre-alarm



Maintenance of the UPS must be performed



Maintenance of the batteries must be performed

Further Faults and Causes

Constant Power Services are always on hand to discuss any potential problems or queries you may have with both existing installations and new. Below we have described some common or possible faults that may occur and the reason for these.

Alarm or Issue

Possible Causes

Mains Failure or Input Switch Open

The UPS is supplying the load from the battery

There is a power cut and the UPS operating correctly

If the UPS displays the input voltage & frequency, check to see whether they are present and correct. If the voltage or frequency is too low or high the UPS will operate on battery.

A Breaker has tripped upstream from the UPS. Check why the breaker has tripped, and if safe to do so reset the switch.

The UPS is alarming bypass fault

The bypass voltage or frequency is out of limits to be able to feed the load:

Check the Bypass voltage & frequency. It is likely either the mains voltage is low or high

The UPS is operating from a generator with unstable frequency or poor quality waveform.

There is a power cut on the bypass supply and the UPS operating correctly

A Breaker has tripped upstream from the UPS. Check why the breaker has tripped, and if safe to do so reset the switch.

The UPS has Asynchronous Alarms

The bypass frequency is out of limits or rapidly changing:

It is likely the UPS is operating from a generator with unstable frequency or poor quality waveform.

Battery not present or fault

The UPS has tested the battery and found some issue so that full autonomy is not available:

There are low battery blocks within the battery.

The battery has been disconnected from the system by the opening or a fuse or switch.

The battery is low following an extended

High Temperature or fan fail

There is a high temperature within the UPS system:

Check the ambient temperature is within the UPS specification.

Check that all the fans are operating correctly

On older UPS systems a excessive temperature can indicate leading power factor outside the UPSs limits (effectively an overload).

There is excess heat being generated by a fault battery, Check the battery and Isolate is necessary


There is an overload on one or more phases of the UPS output:

Check for fan heaters, kettles or other high power items on the UPS output

For three phase UPS Check if the load is balanced evenly across the phases, it may be necessary to move some load to another phase

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