Generator Runs but Has No Power? Causes, Safe Checks and When to Call a Pro
It is one of the more frustrating generator failures: the engine starts, sounds normal, and nothing you plug in turns on. The good news is that the most common causes are simple and safe to check. The less common ones live inside the alternator and involve live voltage, which is where you should slow down. This guide goes from the easy checks to the deeper causes, in order.
Quick answer
- Start with the easy stuff: tripped generator breakers, a tripped GFCI outlet, a bad cord or power strip, an overload or fault light, and a load that is simply unplugged or switched off.
- If you feed the house through a transfer switch or interlock, check that it is set to generator and that the breakers you need are on.
- Inverter generators usually show an overload or fault light; resetting often means shutting down, removing loads and restarting.
- Brushed conventional generators can lose residual magnetism after sitting, and some manufacturers describe a field-flashing procedure. Follow your manual or have a technician do it.
- Do not open the alternator housing or test inside the control panel unless you are qualified. Generator output can kill.
Start with the obvious, in this order
Most "no power" calls turn out to be something outside the alternator. Work through these before assuming the worst.
- Generator circuit breakers. Most generators have one or more breakers on the control panel, sometimes one per outlet group. A tripped breaker may look only slightly different from a closed one. Turn off loads, then reset each breaker firmly, off and back on.
- GFCI outlets. Many portable generators have GFCI-protected receptacles. Press the reset button. If it will not reset, or trips again as soon as you plug in, see our guide to why generator GFCIs keep tripping.
- Overload or fault light. Inverter generators typically have an overload, output or fault indicator. If it is lit, the inverter has shut off output to protect itself. Unplug everything, shut down, restart, and add loads one at a time.
- Your cord and power strip. Plug a simple known-good item, like a work light, directly into the generator. If it works there, the problem is in your cord, strip or the device.
- The load itself. Check that the appliance is on and works on a regular outlet when power returns. Some appliances with electronic controls do not like certain power sources, which is a different problem.
- Economy or idle mode. Eco mode on an inverter lowers engine speed at light load but should not cut output entirely. If output only fails with eco on, note it for service.
If you are feeding the house
When the generator powers circuits through a transfer switch or an interlock and inlet, there are more places for power to stop.
- The transfer switch is set to generator, or the interlock is in the generator position with the main breaker off.
- The generator-feed breaker in the panel is on.
- The individual circuit breakers you want powered are on.
- The inlet cord is fully seated and locked at both ends, and the generator's twist-lock outlet breaker is on.
- The cord itself is undamaged. Twist-lock plugs can look seated without being turned to lock.
Never try to bypass a transfer switch or interlock, and never feed the house through a regular outlet with a double-male cord. Backfeeding can energize utility lines and endanger line workers and neighbors. If the house connection seems wrong, call the licensed electrician who installed it.
Neutral bonding matters here too. Some generators have a bonded neutral and some are floating, and the right setup depends on your transfer equipment. A mismatch is more likely to trip a GFCI than cause zero output, but it is worth understanding. See floating vs bonded neutral.
Testing output without taking risks
To know whether the generator itself is producing power, you need to test at the outlet. The safest tools for most owners are:
- A plug-in outlet tester or a plug-in voltage display, which reads from the receptacle without exposed probes.
- A known-good work light or lamp plugged directly into each outlet group.
- A multimeter used only at the receptacle, if you already know how to use one safely for AC voltage. Do not probe inside the panel.
Test each outlet group, including the 120 V duplex outlets and any twist-lock outlet. If some groups work and others do not, the problem is likely a breaker, outlet or wiring on that group rather than the alternator.
Deeper causes inside the generator
If the engine runs, breakers and GFCIs are fine, and the outlets still read zero, the problem is likely in the power-generating side. What follows explains the common causes so you can talk to a technician; most of these repairs involve live voltage and should be left to someone qualified.
| Cause | Generator type | Typical signs | Who should fix it |
|---|---|---|---|
| Loss of residual magnetism | Many brushed conventional generators | No output after long storage or after running with no load; engine fine | Owner only if the manual describes field flashing; otherwise a technician |
| Worn or stuck brushes | Brushed conventional | Intermittent or no output, often on older units | Technician, or an experienced owner with the service manual |
| Failed AVR (voltage regulator) | Many conventional models | No output, very low or very high voltage | Technician; correct part by model number |
| Failed capacitor | Brushless capacitor-excited designs | No or low output; capacitor may look swollen | Technician (capacitors can hold a charge) |
| Inverter module fault | Inverter generators | Fault light, no output despite reset | Authorized service center |
| Damaged windings or wiring | Any | Burning smell, visible damage, after an overload or water exposure | Technician |
Residual magnetism, explained
Many brushed conventional generators rely on a small amount of magnetism left in the rotor to begin producing voltage each time they start. That residual magnetism can fade if the generator sits for a long time, or if it is shut down with a load still connected. Without it, the engine runs normally but the alternator never "wakes up."
The fix is called flashing the field: briefly applying a small DC voltage to the field to restore the magnetism. Some manufacturers describe how to do it for their models. Because it involves working near live connections, only do it if your manual gives a procedure for your specific model and you are comfortable with it. Otherwise, a small-engine or generator shop can do it quickly.
To help prevent it, turn off loads before shutting the generator down, and run the generator periodically during storage, as our maintenance guides recommend.
Finding the right part
If a technician identifies a failed AVR, capacitor or brush assembly, the correct part depends on the exact model and sometimes the serial range. Our guide to finding replacement parts by model number shows where to find that information.
When it is really an engine problem
Output depends on engine speed. If the engine is running too slowly, surging, or shutting itself off, voltage can be low or missing. Watch for:
- The engine starts, then dies after a few seconds, which often points to the low-oil sensor; see low-oil shutdown troubleshooting.
- The engine hunts up and down, which can make voltage unstable.
- The engine is hard to start or runs rough, covered in troubleshooting a generator that will not start.
Safety while you troubleshoot
Keep the generator outdoors in its safe spot, far from windows, doors and vents, even while troubleshooting, and keep battery-backed CO alarms working inside. Do not move it into a garage to work on it in the dry while it runs. Shut it down and let it cool before touching anything near the engine or muffler, and keep hands away from any exposed wiring when it is running.
FAQ
Why does my generator run but not produce electricity?
The most common causes are a tripped breaker on the generator, a tripped GFCI outlet, an overload shutdown or a bad cord. On brushed conventional generators, loss of residual magnetism after storage is another frequent cause. Failed regulators, brushes or capacitors are less common and need a technician.
How do I reset a generator overload?
Turn off or unplug all loads, reset any tripped breakers, and on inverter models usually shut the generator down and restart it. Then add loads one at a time, largest first. Check your manual for your model's exact reset procedure.
What is flashing the field on a generator?
It is a procedure that briefly applies a small DC voltage to a brushed generator's field to restore lost residual magnetism. Only do it if your manual describes a procedure for your model and you are comfortable with it; otherwise have a technician do it.
Can I test generator output with a multimeter?
If you know how to use a multimeter safely on AC voltage, testing at the receptacle is reasonable. Do not probe inside the control panel or alternator housing. A plug-in outlet tester is a safer option for most owners.
The bottom line
Most no-power problems are breakers, GFCIs, cords or overloads, and you can fix them in minutes. If the outlets still read zero, think residual magnetism on brushed generators, then regulators, brushes, capacitors or inverter modules, and hand those to a qualified technician. Keep the generator outdoors and away from the house the whole time you troubleshoot.