Generator Running but No Power: Troubleshooting in Order

The engine starts and runs smoothly, but nothing plugged into it works. If it won't start at all, that's a different checklist. Here the engine is fine and the electricity isn't getting out.

Short answer: work from the generator outward. Reset the generator's own breakers and GFCI outlets and check its mode switches, then check the cord, the inlet and the transfer switch. If the generator's own outlets still show no voltage with everything reset, the alternator isn't generating. That's usually lost residual magnetism or a failed regulator, brush set or capacitor, and it's service work.

The order to check

The single most useful test sits between steps 2 and 3: is voltage present at the generator's own outlet? That answer tells you which half of the list you're in.

1. The generator's breakers, GFCI outlets and overload light

Most portable generators have circuit breakers on the control panel for their receptacles, and many have a main output breaker as well. A tripped one can look almost identical to a set one, so cycle each fully.

Portable generators typically have GFCI-protected receptacles (NEC 445.20 in recent editions), and a tripped GFCI kills the outlet it protects, sometimes more than one. Press RESET. If it trips again immediately with nothing plugged in, stop and have the generator serviced. If it trips only when the generator is connected to the house wiring, that's a separate problem covered in generator neutral bonding.

Overload indicator. Many inverter generators cut their output after an overload and light a warning while the engine keeps running. Remove load, then reset as the manual describes, often by stopping and restarting the engine.

Don't keep resetting anything that trips again straight away. A protective device that won't hold is reporting a fault.

2. Eco mode and the voltage selector

Voltage selector. Some generators have a switch that sets the output to 120 V only or to 120/240 V. In the wrong position, the outlet you're using may be dead or deliver the wrong voltage. Set it for that outlet as the manual describes.

Eco or idle mode. This lets the engine slow down at light load. It shouldn't remove output by itself, but a large load hitting an idling engine can trip the overload, and some manuals say to switch it off for motor loads. Turn it off while you diagnose.

Is the generator making power at all?

With the engine running and nothing else connected, check one of the generator's own 120 V outlets:

• Plug in a known-good lamp or work light. The simplest test there is.
• Plug in a receptacle tester. One with a voltage display shows the number, not just a light pattern. Some generators show an "open ground" pattern on a three-light tester by design, so don't read that alone as the fault.
• Use a multimeter on AC volts. Expect close to 120 V on a 120 V outlet. On a 120/240 V twist-lock, expect about 240 V between the two hots and about 120 V from each hot to neutral. Probe a live receptacle only if you know how to do it safely; otherwise stick to a plug-in tester on the 120 V outlets.

Voltage present: the generator is working. The problem is downstream, in steps 3, 4 or 7.

No voltage, or only a few volts, with every breaker and GFCI reset: the problem is inside the generator, in steps 5 or 6.

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For the 240 V outlet, a true-RMS multimeter reads the voltage directly:

3. The cord and the connection

Twist-lock plugs must be fully inserted and turned until they lock, at the generator and at the inlet box. A half-seated plug can make poor contact or none.

Inspect the whole cord. A cut or crushed jacket, bent pins, or a melted or discolored plug means stop using it.

Swap in a known-good cord if you have one. Don't open the inlet box.

4. The transfer switch or interlock

This is the usual answer when the generator's outlets have power but the house doesn't.

Interlock kit: the main breaker must be off, the plate slid across, and the generator breaker on. A generator breaker left off is the classic miss.

Manual transfer switch: each circuit you want powered has to be moved to the generator position, and any generator main on the switch has to be on.

The branch circuits themselves: a breaker in the panel for the circuit you're testing can be off or tripped independently of the generator.

If the sequence is right and the house is still dead, suspect a failed switch or a loose connection: a licensed electrician's job, so don't open the panel or the switch. See transfer switch explained.

5. Lost residual magnetism

A conventional generator with a wound field starts making voltage from a small amount of magnetism left in the rotor, and the regulator builds on that to full output. If it fades, the engine runs normally but every outlet reads zero or close to it.

It's commonly lost after long storage, or after the engine is shut down with a load still connected. Disconnecting loads before shutdown is a good habit for this reason.

Restoring it is called field flashing. Do it only by following the manufacturer's documented procedure for your model, or have a service shop do it. An improvised version can damage the regulator.

Inverter generators generally use permanent-magnet alternators, so this cause is unlikely on them. Dead output on an inverter unit points to its protection circuits or the inverter module.

6. Failed regulator, brushes or capacitor

If output is still missing, a part has usually failed:

• Brush-type alternators with an AVR (automatic voltage regulator): worn brushes or a failed AVR give low or no output.
• Brushless, capacitor-regulated designs: a failed capacitor gives low or no output.
• Inverter generators: the inverter module, usually a board-level replacement.
• Any design: a damaged rotor or stator winding.

Diagnosing any of these means testing inside the alternator housing, where terminals carry full output voltage while the engine runs and capacitors can hold a charge after it stops. That's service-shop work.

7. The load itself

A dead appliance looks exactly like a dead generator. Plug a simple, known-good load straight into the generator to rule it out.

Appliances can have their own GFCI, reset button or thermal cutout. A large motor starting on an already busy generator can also trip the overload every time; try it on its own.

Safety while troubleshooting

• Never open the alternator, end cover or control panel with the engine running.
• Keep it outdoors and away from the house while you diagnose, even in bad weather. Never move a running generator into the garage. See carbon monoxide safety.
• Switch the generator's breakers off before plugging or unplugging a cord.
• Never backfeed. A transfer switch that won't pass power is not a reason to plug the generator into a dryer or range outlet. See backfeeding dangers.

Standards and code reference

The standards behind this guide, for looking up in the edition your jurisdiction has adopted:

• NEC 445.20: GFCI protection for receptacles on portable generators rated 15 kW or smaller
• NEC 250.34: grounding of portable generators
• NEC 702.5: transfer equipment required before a generator feeds premises wiring

Code editions and local amendments vary. Confirm the adopted edition with your AHJ, and treat manufacturer instructions as governing wherever they are more restrictive.

Where to go next

• Generator won't start: troubleshooting in order
• Transfer switch explained
• Generator inlet box
• Generator maintenance schedule
• Size it properly: generator sizing calculator

More in our generator and backup power guides.