Generator Running But No Power: Causes and Fixes
The engine is running smoothly, but nothing works when you plug in. This is almost always an electrical problem rather than an engine problem. Many causes take a minute to check, such as a tripped breaker or GFCI. The rest involve the alternator, and some of those need a technician. This guide walks through them in the order you should check.
Safety: run the generator outdoors only. Do not open the generator’s control panel or alternator while it is running, and do not touch internal wiring. Use a multimeter only if you know how to measure AC voltage safely.
Quick diagnosis
| What you measure or see | Likely cause | Next step |
|---|---|---|
| No power at outlets, breaker looks tripped | Tripped breaker or GFCI | Reset after removing loads |
| Voltage near zero (a few volts) | Lost residual magnetism, failed capacitor or brushes | Technician or manual procedure |
| Voltage low (about 60 to 100 V on 120 V outlets) | Engine running slow, worn alternator, bad capacitor | Check engine speed, then service |
| Voltage high (above about 130 V) | Failed voltage regulator (AVR) or governor set too fast | Shut down. Do not use appliances. Service needed |
| Voltage normal at generator, no power in the house | Transfer switch, interlock, inlet or cord problem | Check the connection method |
Step 1: Check breakers and GFCI outlets
- Look at the circuit breakers on the generator panel. A tripped breaker may sit between ON and OFF. Push it fully to OFF, then back to ON.
- Many generators have GFCI outlets. Press the RESET button. A GFCI can trip because of moisture, a damaged cord or a ground fault in an appliance.
- If a breaker trips again immediately, unplug everything, reset, and add loads one at a time to find the one that causes it. See generator overload and tripping breakers.
Step 2: Check for an overload or protection mode
Inverter generators have an overload indicator and sometimes a separate “AC output” light. If the overload light is on, turn off the generator, unplug everything, restart and add loads gradually. Some generators also shut off AC output when the oil is low, when they overheat, or when a carbon monoxide sensor trips.
Step 3: Check switches and outlets
- Dual-voltage generators have a selector for 120 V only or 120/240 V. Make sure it is set correctly and that you are using the right outlet.
- Some models have an economy or eco switch. Try it both ways.
- Try a different outlet on the generator and a different device, preferably a simple lamp, to rule out a dead outlet or a faulty appliance or cord.
- Extension cords wear out. Replace any with damaged insulation. Make sure the cord gauge is heavy enough for the load.
Step 4: Check the engine speed
Alternator output depends on engine speed. Most 60 Hz portable generators run at about 3,600 rpm. If the engine is hunting, bogging or running slowly, voltage will be low. Fix the engine problem first. See our guides on surging and stalling.
Step 5: Measure the voltage
With the generator running and no load, use a multimeter set to AC volts at an outlet. A healthy generator should read close to 120 V on a 120 V outlet and about 240 V across the two hot slots of a 240 V outlet. Within about 5% (114 to 126 V and 228 to 252 V) is normal.
- Near zero volts: the alternator is not producing output. Jump to the next section.
- Normal at no load but collapses with a small load: the engine may be weak, or a capacitor or winding is failing.
- Much too high: the voltage regulator is not working. Stop using the generator and have it serviced to protect your appliances.
Alternator causes
Lost residual magnetism
Brush-type and some capacitor-type alternators rely on a small amount of magnetism left in the rotor to start producing voltage. Long storage, dropping the generator or running it without a load for a long time can cause that magnetism to fade, leaving the generator running with only a few volts at the outlets. Technicians restore it by briefly applying direct current to the field winding, a procedure called field flashing. The correct method varies by model, so follow your service manual or use a technician.
Failed capacitor
Many brushless portable generators use a capacitor to excite the alternator. When it fails, the generator runs but produces little or no voltage. Replacement capacitors are inexpensive, but the correct specification matters.
Worn brushes or slip rings
Brush-type alternators wear over time. Worn brushes lose contact and reduce or stop output.
Failed voltage regulator (AVR) or winding
The automatic voltage regulator keeps voltage steady. If it fails, output may be erratic, too low or too high. A shorted or open stator winding can cause no output. These are repairs for a technician and may be worth weighing against the cost of a new generator on older, small units.
If you have power at the generator but not in the house
- Check that the generator breaker is on and the main breaker is off, if you are using an interlock kit.
- Check the inlet box connection and the power cord, and that the cord matches the generator outlet.
- Check that the transfer switch is in the generator position and that its circuits are turned on.
- If you are connecting without a transfer switch, read our guide on safe ways to connect a generator to a house. Never backfeed through a wall outlet.
Frequently asked questions
Why does my generator run but have no power?
Start with the breaker, GFCI and overload protection. If those are fine, the cause is typically a failed capacitor, loss of residual magnetism, worn brushes or a failed regulator.
How do I reset a generator breaker?
Turn off the connected loads. Press the breaker fully to OFF, then to ON. If it trips again, there is a short or overload.
Can a generator lose its power from sitting?
Yes. A generator that has been stored for a long time can lose residual magnetism, so it runs but makes no power. Running it under load for 20 to 30 minutes every month helps prevent that, as does proper storage.
Is it worth repairing?
For larger or newer units, yes. For old small portables, compare the repair cost to a replacement. Repair estimates are easiest to judge once a technician has tested the alternator.
Related guides and tools
Electrical work can be dangerous. If you are not confident testing or repairing a generator’s electrical components, use a qualified technician.
