Vacon VFD Fault Codes — Complete Troubleshooting Guide

Vacon drives — now part of the Danfoss portfolio after the 2014 acquisition — use a two-layer fault system: a Fault Code (F1, F2, F3…) that tells you the category, and either a Subcode (NXP/NXS series) or Fault ID (Vacon 100 series) that tells you the exact cause. Skipping the subcode and jumping straight to “F1 Overcurrent = bad motor” is how you replace parts that don’t need replacing. This guide covers both layers for Vacon 100 FLOW/INDUSTRIAL/HVAC, Vacon NXP, and Vacon 10.

How Vacon Fault Numbering Works

Critical rule: A fault trips the drive and stops the motor. An alarm is a warning only — the drive keeps running but you need to act.

Accessing Fault History

Vacon NXP / NXS

1. Navigate to Main Menu → M4 Fault History
2. Press the right arrow to enter
3. Last 30 faults stored with timestamps (operating hours) and drive state at trip

With NCDrive PC software (preferred method):

• Connect via RS-232 service port or USB-RS232 adapter
• Open Fault History view — shows fault code, subcode, operating hours, frequency, current, and voltage at time of trip
• Datalogger can be pre-triggered to capture pre-fault signals

Vacon 100 INDUSTRIAL

1. Navigate to Main Menu → Diagnostics → Fault History
2. Last 40 faults with Real-Time Clock timestamps
3. Record the Fault ID before resetting — the ID is the specific cause, not just the category

Vacon 10

1. Press MENU until you reach F — (Fault History)
2. Browse with UP/DOWN arrows
3. Stores last 5 faults

F1 — Overcurrent

Display: F1 (NXP: followed by S1–S4 subcode; Vacon 100: followed by ID 1 or ID 2)

Meaning: Motor phase current exceeded the instantaneous trip threshold (approximately 4× rated drive current).

NXP Subcodes:

Causes (in order of likelihood):

1. Short circuit in motor cable or motor winding — most common
2. Acceleration time too short — motor draws excessive current during ramp-up
3. Sudden heavy load increase (e.g., jam in pump or fan)
4. Motor incorrectly sized for the drive
5. Motor parameter identification not run (drive using wrong current model)

Diagnosis Steps:

1. Disconnect the motor cable at the drive output terminals (U, V, W)
2. Attempt a no-load run — if F1 still appears, the fault is in the drive itself (IGBT failure)
3. If no-load run is clean: reconnect motor and check cable for phase-to-phase or phase-to-ground short with a megohmmeter (>1 MΩ at 500V DC)
4. Check motor nameplate data against drive parameter settings (nominal current, voltage, frequency, power)
5. Run motor parameter identification: navigate to M7 → Identification Run — run at standstill if the load can’t be disconnected

Fix:

• Clear short circuits in cable or motor
• Increase acceleration time (parameter P3.4.1.2 on Vacon 100, or application-specific accel time on NXP)
• Run motor identification after correcting motor parameters

F2 — Overvoltage

Meaning: The DC link voltage exceeded the hardware trip threshold. For 400V input drives, this is typically 840V DC. For 500V drives: 911V DC. For 690V drives: 1,200V DC.

NXP Subcodes:

Causes (in order of likelihood):

1. Deceleration time too short — regenerative energy from the motor charges the DC bus
2. High supply voltage spikes from the grid
3. No braking resistor or brake chopper not enabled when running high-inertia loads
4. Overvoltage controller disabled (parameter not activated)
5. Load is generative (e.g., crane lowering, downhill conveyor)

Diagnosis Steps:

1. Measure input voltage at the drive terminals — should be within +10% of nominal
2. Check whether F2 occurs on deceleration specifically (confirms regenerative braking cause)
3. On NXP: Check parameter P2.6.5.1 (overvoltage controller) — should be 1 or 2 for most applications
4. If braking resistor is installed: measure resistance value and compare to specifications; check wiring

Fix:

• Increase deceleration time (P3.4.1.3 on Vacon 100, or application-specific decel time)
• Enable overvoltage controller: set to 1 (no ramp, P-type) or 2 (with ramp, PI-type) on NXP
• Install braking resistor and chopper for high-inertia loads
• For continuous regenerative loads (cranes, compressors): consider AFE (Active Front End) unit

Parts needed: Braking chopper module (VBRC series, drive-specific), braking resistor (sized per application load calculation)

F3 — Ground Fault (Earth Fault)

Meaning: The sum of the three phase currents is not zero, indicating current is flowing to ground through an insulation fault.

Causes (in order of likelihood):

1. Insulation failure in motor cable — especially on long cable runs with moisture ingress
2. Motor winding insulation degraded — common in older motors or after thermal stress
3. dU/dt or sine wave filter malfunction (if installed between drive and motor)
4. Cable routed through conduit with damaged sections

Diagnosis Steps:

1. Disconnect the motor and motor cable at the drive output
2. Megohmmeter test the motor cable: each phase to ground at 500V DC — should be >1 MΩ
3. Separately megohmmeter test the motor windings: each winding to frame at 500V DC
4. If both test clean: inspect the dU/dt or sine filter if one is installed

Fix:

• Replace damaged motor cable — use VFD-rated cable with symmetrical shielding
• Rewind or replace motor if insulation resistance is below 1 MΩ
• Ensure cable shield is properly terminated at both ends (motor frame and drive PE terminal)

Note: On IT (floating/ungrounded) networks, the F3 threshold may need adjustment — consult the NXP application manual for the earth fault supervision parameter.

F5 — Charging Switch Fault

Meaning: The DC bus precharge circuit did not complete correctly. The drive sent a start command but the charging switch status feedback indicated the switch is still open.

Causes:

• Defective precharge relay or thyristor
• Wiring fault on the charging switch feedback signal
• Damaged charging resistor (NXP larger frames use a separate resistor)
• Control board communication fault with the power board

Diagnosis Steps:

1. Power off and wait 5 minutes for DC bus to discharge fully
2. Inspect the precharge circuit board in the power unit (typically in the rectifier section)
3. Check the feedback signal wiring between the power board and control board

Fix:

F5 almost always requires power unit inspection or replacement. Reset the fault and restart once — if it returns immediately, do not continue cycling power. Contact your Danfoss distributor with the full fault history.

F6 / F9 — Undervoltage

Display: F9 on NXP (Vacon 100 uses F9, ID 80)

Meaning: The DC link voltage dropped below the minimum operating threshold during run. For 400V drives, this is typically below 330V DC.

NXP Subcodes:

Causes (in order of likelihood):

1. Supply voltage sag or momentary interruption (most common on HVAC/pump applications)
2. Blown input fuse
3. Input contactor opened during run
4. Supply voltage too low (utility problem or transformer undersized)
5. Internal precharge fault (F5 and F9 appearing together)

Diagnosis Steps:

1. Check input voltage with a power quality meter — look for sags during startup of large motors on the same circuit
2. Check input fuses — use a DMM to verify continuity with the drive powered down
3. If F9 appears at startup only: the precharge may not be completing before the run command

Fix:

• Verify supply voltage is within drive specification (typically +10/-10% of nominal)
• Replace blown input fuses (use semiconductor-type fuses on larger drives)
• For frequent voltage sags: enable undervoltage restart (auto-restart parameter)
• Install line reactor on input to buffer voltage transients

F7 — Motor Overtemperature (Calculated)

Meaning: The drive’s internal thermal model has calculated that the motor has exceeded its thermal limit. This uses the measured current profile over time — it does not require a physical temperature sensor.

Causes:

1. Motor overloaded — running at above 100% rated current for extended periods
2. Motor cooling fan not running (on externally-cooled motors)
3. Motor thermal model parameters incorrect (wrong motor data entered)
4. Duty cycle too heavy for motor thermal class

Diagnosis Steps:

1. Check motor current on the drive display — compare to motor nameplate rated current
2. Verify motor thermal protection parameters match the nameplate (nominal current, motor thermal time constant)
3. On externally-ventilated motors: confirm the cooling fan is running at full speed

Fix:

• Reduce motor load or increase motor/drive sizing
• Correct motor parameter data in the drive (run motor identification)
• For motors with PT100 or PTC thermistors: use the physical sensor input (F29/F56) rather than relying solely on the calculated model

Parameter to check: Motor nominal current (must match nameplate exactly), motor thermal time constant

F8 — System Fault

Meaning: F8 is a wrapper code for internal drive faults. The subcode (S1–S50 on NXP, specific IDs on Vacon 100) identifies the actual problem.

Critical Subcodes:

For F8 S30 (most common on new installations): The Safe Torque Off (STO) system requires both channels to be in the same state. If STO is not being used, both SD1 and SD2 terminals must have +24V (or use the factory jumper). If one channel is active and the other isn’t, F8 S30 trips.

F9 — Underload (Motor Underload Protection)

Note: On NXP this is Fault 17 (Motor Underload). On Vacon 100 it is F17. Do not confuse with F9 Undervoltage.

Meaning: The motor is drawing significantly less current than expected for its speed. This protects processes where a drop in load indicates a problem (broken belt, empty pump, conveyor jam).

Causes:

1. Pump running dry — cavitating or no fluid in the system
2. Drive belt broken on a fan or blower
3. Coupling sheared between motor and load
4. Underload protection parameters set too aggressively for the application

Diagnosis Steps:

1. Check if the connected load is actually turning — verify mechanically
2. On pump applications: check suction strainer and verify fluid supply
3. Review underload protection parameters — the underload curve can be adjusted to reduce false trips

Fix:

• Restore the load (fix the belt, prime the pump, etc.)
• If false trips are frequent: adjust the underload protection minimum torque threshold and delay time

HVAC application note: Underload protection is extremely useful on AHU (Air Handling Unit) applications — an F17/F9 underload during normal operation almost always means a broken fan belt.

F10 — Input Phase Loss

Meaning: One of the three supply phases is missing or significantly unbalanced.

Causes:

1. Blown main input fuse on one phase
2. Open phase in the supply cable
3. Contactor with one welded-open contact
4. Supply transformer with a failed winding

Diagnosis Steps:

1. Measure all three input voltages at the drive input terminals with the drive powered (use a DMM with clamps on the input terminals while power is live — use appropriate PPE)
2. Compare L1-L2, L2-L3, L1-L3 — all should be within 3% of each other
3. Check input fuses with a DMM after powering down

Fix:

• Replace blown fuse (use semiconductor-type HRC fuses on the drive input)
• Repair or replace supply cabling if open phase found

Note: Vacon drives will typically show F10 as an alarm/warning (A10) before it trips as a fault, giving you a window to investigate before the drive shuts down.

F14 — Drive Overtemperature

Meaning: The heat sink temperature exceeded the trip threshold. For most 400V drives: >90°C (194°F). For 690V FR6 frames: >77°C (171°F).

NXP Subcodes:

Causes (in order of likelihood):

1. Cooling fan failed or clogged with dust
2. Ambient temperature too high (above rated 40°C / 104°F without derating)
3. Switching frequency set too high for the load and ambient temperature
4. Heat sink fins clogged with debris
5. Incorrect mounting (inadequate clearance above/below drive)

Diagnosis Steps:

1. Open the drive enclosure door and listen for the cooling fan — on smaller drives it runs continuously; on larger ones it cycles
2. Inspect heat sink fins — use compressed air to clear debris
3. Measure ambient temperature at the drive intake
4. Check switching frequency parameter — some applications run with higher-than-necessary switching frequencies

Fix:

• Replace cooling fan (common failure on drives >5 years old)
• Add forced ventilation to the enclosure
• Reduce switching frequency (costs slightly higher motor noise, saves drive temperature)
• For liquid-cooled NXP: check coolant flow rate and inlet temperature

Parts needed: Cooling fan (Ebm-papst or equivalent, frame-specific), IP54 door fan kit for sealed enclosures

F22 — Parameter Fault

Meaning: A checksum error in the drive’s parameter storage. Parameters may be corrupted or inconsistent.

Causes:

• Power loss during a parameter save operation
• Memory chip degradation (older drives)
• Parameter conflict from software download

Fix:

1. Note any custom parameter settings first (or use NCDrive to upload/download parameter files)
2. Reset factory defaults: navigate to System Menu → Load Factory Defaults
3. Re-enter critical parameters (motor data, application settings, I/O assignments)
4. If fault persists: the control board may need replacement

F29 — Thermistor Fault (Option Board Input)

Meaning: The thermistor input on an option board (typically OPTAF) detected motor overtemperature OR the input is open-circuit when it should be connected.

Critical Note for Unused Thermistor Inputs:

If the thermistor function is not used and the OPTAF board is installed, the thermistor input terminals must be short-circuited (jumpered). An open-circuit input will read as infinite resistance, which the drive interprets as a tripped thermistor (motor too hot).

Causes:

• Motor thermistor (PTC) has reached trip temperature
• Thermistor cable disconnected or broken
• Thermistor input not short-circuited when unused
• Thermistor short circuit (NXP S1: hardware short circuit on the input)

Diagnosis Steps:

1. Measure thermistor resistance at the motor: cold motor PTC should read <1500 Ω; >4000 Ω indicates trip
2. Check cable from motor to drive for continuity and shorts
3. If not using a physical thermistor: verify terminals are jumpered

F52 — Keypad / Panel Communication Fault

Meaning: Communication between the keypad and the drive control board was lost.

Causes:

• Keypad cable disconnected or damaged
• Panel connected and then removed during operation (if configured as the control source)
• EMI interference on the keypad cable in noisy installations

Fix:

• Reconnect or replace the keypad cable
• If control is from remote I/O (not keypad), ensure the control source parameter is set correctly — the drive should not trip on keypad loss if keypad isn’t the active control source

F53 / F54 — Fieldbus and Slot Faults

F53 — Fieldbus Communication Fault: The fieldbus master (PLC) has not communicated with the drive within the watchdog timeout.

Causes:

• PLC program stopped or in stop mode
• Fieldbus cable disconnected
• Wrong drive address or baud rate
• Fieldbus terminating resistors missing

F54 — Slot Fault: An option board in a drive slot failed or was removed.

Fix for F54 when board was intentionally removed: Navigate to the System Menu and acknowledge the hardware change to clear the fault. The drive retains the slot configuration until explicitly reset.

Accessing Parameters: Lock/Unlock

Vacon NXP / NXS — Parameter Lock

• Navigate to M7 → System → Password
• Default password: 0
• Enter password to unlock write access

Vacon 100 — Parameter Lock

• Navigate to Main Menu → System → Security → Password
• Locked parameters show a padlock icon on the keypad
• Can also be controlled via digital input (Parameter Lock DI)

Fault History Access — Step by Step

Vacon NXP via Keypad:

1. From main display: press right arrow
2. Navigate to M4 (Fault History)
3. Enter the menu — shows F-codes, subcodes, and drive state at trip

Vacon 100 via Keypad:

1. Press MENU
2. Navigate to Diagnostics → Fault History
3. Scroll through entries — each shows Fault Code, Fault ID, timestamp, and frequency/current/voltage at trip

Via NCDrive (NXP) or VACON Live (Vacon 100):

Both PC tools provide far more detail than the keypad and allow parameter backup before major troubleshooting. Connect via the RS-232 service port (RJ45 to DB9 adapter, 9600 baud, 8-N-1).

HVAC and Pump Application Notes

Vacon 100 FLOW/HVAC drives are optimized for fan and pump applications. Common HVAC-specific issues:

Parts Reference Table

Quick Fault Reference

When contacting Danfoss/Vacon technical support, provide: drive model number (from the nameplate), firmware version (from the system menu), the complete fault history list including all subcodes/IDs, and the application parameters file if available from NCDrive or VACON Live.

Where to Buy Replacement Parts

Find replacement parts for Vacon (Danfoss) VFDs on Amazon:

• Vacon Danfoss VFD Drive Replacement Parts
• Danfoss VFD Cooling Fan Replacement
• VFD Option Card & Fieldbus Module