Key takeaways
A variable frequency drive that refuses to start stops a line cold, and the pressure to get it running fast is exactly when technicians start swapping parts at random. A VFD is a logic device as much as a power device, so the fastest path back to production is a structured walk through what the drive needs before it will turn a motor. This guide gives you that order.
Before touching a single wire, read the keypad or HMI. The drive is telling you which half of the problem you have.
Safety first: drive troubleshooting is electrical work for qualified people only. Live measurements at the input terminals need the arc flash PPE your site requires and a meter rated for the circuit. Before you open the enclosure or touch motor wiring, lock out and tag out the supply, wait the capacitor discharge time printed on the drive, and verify zero volts with a meter you have just tested on a known live source. Never insulation test a motor with the cable still connected to the drive, and never jumper STO or an interlock to test a start.
Verify three-phase input voltage at the drive terminals on all three phases, and confirm it is within the drive's rated range. A blown input fuse, an open disconnect, a tripped upstream breaker, or a lost phase will leave the drive dark or unable to charge its DC bus. Some drives also use a separate control-power supply for the logic board and keypad, so check that too. If the display is blank, this step is your whole problem.
If a fault code is present, that code is your fastest diagnostic. Undervoltage, overcurrent, overvoltage, ground fault, and overtemperature each point to a specific cause and check. Our fault-specific guides walk through the common ones, and manufacturer references such as the ABB VFD fault codes and Yaskawa VFD fault codes lists translate the code on your screen into a root cause. Clear the fault, fix the cause, and only then attempt a restart.
A drive only starts from the source it is configured to obey. If the control source is set to the keypad, terminal input, or a fieldbus, a start command from anywhere else does nothing. Check that:
Modern drives ship with a safe-torque-off (STO) input that must be energized before the drive will produce any output. On the bench it is often jumpered; in the field it is wired through a safety relay or E-stop chain. If STO is open, the drive will not start, and the display usually shows a dedicated code for it: for example Hbb on a Yaskawa, F059 Safety Open on a PowerFlex 525, or 5091 or A5A0 on an ABB ACS880. Confirm STO terminals are energized, then verify any external run-permissive, E-stop, or interlock in the control chain is closed.
A valid run command with a zero speed reference produces a running-but-0 Hz state that looks like a no-start. Check the frequency reference source (keypad setpoint, analog input, preset speed, or network value) and confirm it is actually delivering a value above the minimum frequency. A disconnected analog signal, a potentiometer at zero, or a network reference stuck at 0 will keep the motor still.
Many drives have a local/remote toggle and a parameter lock. If the drive is in local mode, remote commands are ignored, and the reverse is also true. A parameter lock or a run-inhibit setting can also block starting. Confirm the mode matches your intended control and that no lockout, keypad-stop latch, or "coast-to-stop pending" state is active.
If every input checks out and the drive still will not start or trips instantly on start, look downstream. An open motor lead, a disconnected output contactor, a shorted or grounded motor, or wildly wrong nameplate parameters can prevent a successful start or cause an immediate trip. Before you touch the motor leads, lock out and tag out the drive supply, wait the capacitor discharge time printed on the drive (ABB, for example, specifies five minutes), and prove zero volts at the input, DC bus and output terminals with a tested meter. Then confirm the motor connections and, if the drive trips the instant you command run, treat it as an output or motor fault rather than a control problem.
| What you see | Likely cause | First check |
|---|---|---|
| Blank display | No input or control power | Input voltage on all three phases; control-power supply; upstream fuse and disconnect |
| Fault code shown | A specific protection tripped | Look up the exact code; fix the cause before resetting |
| "Ready" or "Stopped", nothing on start | Run command not received, or STO open (look for a code such as Hbb, F059, 5091 or A5A0) | Command source parameter; voltage at the run input; safe-torque-off energized |
| Runs at 0.0 Hz | Zero speed reference | Reference source; analog input or setpoint value above minimum frequency |
| Starts, then trips instantly | Output or motor fault | Motor leads and insulation (after lockout, with the motor cable disconnected from the drive); nameplate parameters; ground fault |
| Ignores keypad or remote | Wrong local/remote mode or lockout | Local/remote toggle; parameter lock; run-inhibit |
The single most useful distinction is whether the drive reports a fault. A fault means the drive attempted to act and its own protection stopped it, so the problem is usually electrical or mechanical: voltage, current, temperature, or the motor. No fault plus no motion means the drive is waiting on you: a command, a permissive, or a reference it never received. Sorting every no-start into one of these two paths keeps you from chasing power problems when the real issue is a jumper, and from re-checking wiring when the drive is quietly protecting itself. A shorted or overheating motor is a common downstream cause worth ruling out early; see our guide on electric motor overheating causes, and remember that a voltage imbalance on the three-phase supply can trip a drive on start.
No-start calls repeat when the control logic lives only in one technician's head. A few habits remove most of them:
Tying this to your maintenance system matters because a VFD no-start is rarely just an electrical event; it is a work order, a downtime record, and a clue about an asset that may be drifting toward a bigger failure. Capturing drive behavior alongside the rest of an asset's history is exactly what a modern maintenance platform is for, and pairing it with real-time machine monitoring turns a slow no-start hunt into a targeted fix.
EF does not mean the same thing on every drive, so read the fault list for your exact model. On a Yaskawa drive, plain EF is the minor fault Forward/Reverse Run Command Input Error: the forward and reverse run inputs were both closed for longer than 0.5 seconds, and the motor ramps to stop. Nothing external has failed. Check the run command sequence from the PLC or selector switch so forward and reverse can never be closed at the same time.
Yaskawa EF1 to EF7 are different: an external fault at multi-function input S1 to S7, from a terminal set to H1-xx = 20 to 2F. Find the device wired to that terminal, remove the cause, then reset. If the code points at a terminal with nothing connected, Yaskawa's remedy is to check for unused terminals set to H1-xx = 20 to 2F and change their setting.
"Ready" means the drive is healthy and waiting for a valid run command and speed reference. The most common causes are a command source set to the wrong input, a run signal that is not actually energized at the terminal, an open safe-torque-off input, or a zero speed reference. Work those four items before suspecting the drive itself.
Safe-torque-off (STO) is a safety input that must be energized before the drive can produce output to the motor. If the STO terminals are open, whether from a safety relay, an E-stop, or a missing jumper on the bench, the drive will not start, and the display usually shows a dedicated STO code such as Hbb, F059 or 5091. Confirming STO is energized is one of the first checks on any no-start.
It is a running state with no output frequency, which usually means the drive received a run command but a zero speed reference. Check the reference source, whether that is the keypad setpoint, an analog input, a preset speed, or a network value, and confirm it is delivering a value above the drive's minimum frequency.
No. A fault on start is the drive protecting itself, and repeatedly resetting into a real fault can damage the drive or the motor. Read the exact fault code, diagnose and fix the cause, and only then attempt a restart. If the drive trips the instant you command run, treat it as an output or motor problem.
Read the display. A fault code means the drive acted and its protection stopped it, so look at power, current, temperature, or the motor. No fault and no motion means the drive is waiting on a command, a permissive, or a reference it never received. That one distinction routes almost every no-start to the right half of the problem.
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