51Fault

Felicity inverter error 51 (F51)

INV soft start failure

Also displayed as F51 on some models.

Fault — the inverter cuts its output and the red LED stays solid until the fault is cleared.

The exact meaning depends on your model:

IVGM5KL-P1G1

InverterFault

Also applies to:IVGM6KL-P1G1IVGM7K6L-P1G1IVGM8KL-P1G1

What it means

INV soft start failure — Inverter soft start failure.

Cause: The inverter stage failed to ramp its output up to the working point during soft start — an internal fault rather than a wiring issue.

How to fix it

  1. Restart the system 2~3 times
  2. If the fault still exists, please contact us for help.

Source: Felicitysolar IVGM Series Hybrid inverter Instruction Manual.pdf, p.54

T-REX-3KLP1G01

InverterFault

Also applies to:T-REX-3K6LP1G01T-REX-4KLP1G01T-REX-4K6LP1G01T-REX-5KLP1G01T-REX-6KLP1G01

What it means

BMS doesn't allow inverter to discharge battery

Cause: The battery's BMS is refusing discharge — it has signalled over the communication link that the pack must not be drawn down, and the inverter stops discharging automatically.

How to fix it

Restart the unit, if the error persists, contact the repair center.

Source: T-REX-3_3.6_4_4.6_5_6KLP1G01-hybrid-inverter-user-guide-English.pdf, p.37 · T-REX-3_3.6_4_4.6_5_6KLP1G01-hybrid-inverter-user-guide-English.pdf, p.39

T-REX-10KHP3G01

InverterFault

Also applies to:T-REX-10KLP3G01

What it means

DSP1 communication failure

Cause: Communication has been lost between the inverter and a peripheral device — typically a battery BMS, smart meter, or external monitoring dongle.

How to fix it

Restart the unit, if the error persists, contact the repair center.

Source: T-REX-10KHP3G01-Inverter-User-Guide.pdf, p.29 · T-REX-10KLP3G01-Inverter-User-Guide.pdf, p.29

T-REX-50KHP3G01

InverterFault

What it means

Grid Overvoltage Fault — The grid voltage is too high, check whether the grid voltage is within the normal range.

Cause: The grid voltage measured at the AC terminals is above the inverter's permitted operating window, so it disconnects until the grid returns to range.

How to fix it

  1. Power down the inverter, wait 5 minutes for capacitors to discharge, then restart.
  2. If the fault recurs immediately or repeatedly, record the exact code and contact your installer or the manufacturer's service line.

Source: T-REX-50KHP3G01-user-manual-.pdf, p.47

Apollo-5KLP1G01-MX

Energy storage systemCritical

Also applies to:Apollo-5KLP1G01-M1Apollo-5KLP1G01-M2Apollo-4K6LP1G01-MXApollo-4K6LP1G01-M1Apollo-4K6LP1G01-M2

What it means

DSP1 communication failure

Cause: DSP1 communication failure.

How to fix it

Restart the unit, if the error persists, contact the repair center.

Source: Apollo-5KLP1G01-All-in-one-ESS-User-Guide.pdf, p.44

Frequently asked questions

What does error 51 mean on a Felicity inverter?
It depends on the model — 6 devices use code 51. On the IVGM5KL-P1G1 it means: INV soft start failure. The card for each model on this page gives its exact meaning and fix.
Is error 51 a fault or a warning?
51 is a fault code: the inverter cuts its output and the red LED stays solid until it is cleared.
How do I clear or fix error 51?
1. Restart the system 2~3 times; 2. The exact steps for each affected model are listed on this page.

Related error codes

Other codes on the IVGM5KL-P1G1

All IVGM5KL-P1G1 codes

Other codes on the T-REX-3KLP1G01

All T-REX-3KLP1G01 codes

Other codes on the T-REX-10KHP3G01

All T-REX-10KHP3G01 codes All T-REX-10KLP3G01 codes

Other codes on the T-REX-50KHP3G01

All T-REX-50KHP3G01 codes

Other codes on the Apollo-5KLP1G01-MX

All Apollo-5KLP1G01-MX codes

Prefer the full written guide? Read the complete Felicity inverter error-code guide

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