Critical

F21

OP current sensor failed.

7 Devices that report this code

What does the F21 error code mean?

F21 on a Felicity unit indicates: OP current sensor failed.. It is a critical-severity event that can appear on 7 different devices in the Felicity catalog. The same code may have slightly different recommended fixes depending on the device — the per-device sections below show the exact wording from each device's official manual.

This is a critical-severity code

Critical codes trip the unit offline immediately. They typically indicate hardware failure (short-circuit, IGBT, BMS) or an unsafe operating condition. Do not bypass the fault — note the code and contact authorized service.

What triggers this code

F21 is triggered when the unit's protection or monitoring logic detects the specific condition described above. The exact trigger depends on the device — see the per-device sections for the official manual entry for each.

Apollo-5KLP1G01-MXEnergy storage system↗ view on device
F21OP current sensor failed.Critical
Description

Output current sensor failed.

Cause

Output current sensor failed.

Recommended fix

Output current sensor failed.

Source:Apollo-5KLP1G01-All-in-one-ESS-User-Guide.pdf · page 43
IVEM 6048Inverter↗ view on device
F21The inner temperature over.Fault
Description

Fault: The inner temperature over.

Cause

The inner temperature is over the limitation.

Recommended fix

Check whether the air flow of the unit is blocked or whether the ambient temperature is too high.

Source:felicitysolar IVEM 6048 Solar Inverter User Guide.pdf · page 37
IVEM8048-IIInverter↗ view on device
F21The inner temperature over.Fault
Description

Fault: The inner temperature over.

Cause

The inner temperature is over the limitation.

Recommended fix

Check whether the air flow of the unit is blocked or whether the ambient temperature is too high.

Source:IVEM8K-12K-II_compressed.pdf · page 44
IVEM8048-LVInverter↗ view on device
F21The inner temperature over.Fault
Description

The inner temperature over.

Cause

The inner temperature is over the limitation.

Recommended fix

Check whether the air flow of the unit is blocked or whether the ambient temperature is too high.

Source:FelicitySolar IVEM8048-LV Single Phase Hybrid Inverter User Guide.pdf · page 38
T-REX-10KHP3G01Inverter↗ view on device
F21OP current sensor failed.Fault
Description

Output current sensor failed.

Recommended fix

Output current sensor failed.

Source:T-REX-10KHP3G01-Inverter-User-Guide.pdf · page 28
T-REX-10KLP3G01Inverter↗ view on device
F21OP current sensor failed.Fault
Description

Output current sensor failed.

Cause

Output current sensor failed.

Recommended fix

Output current sensor failed.

Source:T-REX-10KLP3G01-Inverter-User-Guide.pdf · page 28
T-REX-50KHP3G01Inverter↗ view on device
F21Battery 2 software overcurrent fault.Fault
Description

Battery 2 current is too large, check the battery charge and discharge power.

Source:T-REX-50KHP3G01-user-manual-.pdf · page 46

Frequently asked about F21

What is the F21 error on Felicity?
F21 on a Felicity unit means: OP current sensor failed.. It can appear on 7 different devices in the Felicity catalog. The cause and recommended fix are listed for each device on this page.
Can I clear the F21 code myself?
It depends on the severity. Warning-level codes can usually be cleared by following the recommended fix. Fault and critical codes often require checking the source condition first; if the code returns immediately after restart, escalate to authorized service.
Is the F21 fix the same on every device?
The cause is consistent — it's the same protection logic. The exact fix wording can differ per device because each official manual addresses model-specific context (input ranges, parallel-config notes, firmware revisions). Use the per-device section that matches your unit.
Where does this information come from?
Every entry is sourced directly from the official Felicity user manual for the affected device. The "Source" line at the bottom of each device's section shows the manual filename and page number.

Compiled from official Felicity user manuals. Always consult your device manual and a qualified technician before performing repairs.