Why Does My Generator Keep Shutting Off? 10 Causes and Fixes

A generator that runs for a few seconds, a few minutes or a few hours and then quits is usually protecting itself, or it is slowly being starved of something. The timing of the shutdown is the biggest clue, so note how long it runs before it stops and whether it stops cleanly or dies with a stumble.

1. Low oil, or the low-oil sensor

Signs: starts, runs 5 to 15 seconds, stops cleanly. May show a low-oil light.

Check the dipstick on flat ground and fill to the mark. Air-cooled engines use oil, and a long run can take the level below the sensor. If the oil is correct and the generator is on a slope, move it: the sensor reads level, not quantity. If the oil is correct on flat ground and it still dies, the sensor may have failed, which a shop can confirm by disconnecting it as a test.

2. Overload

Signs: stops or the breaker trips when a load is switched on, or the engine bogs down and the output cuts out.

Motors need two to three times their running watts to start. A refrigerator and a well pump starting together can exceed the generator’s surge rating. Reset the breaker, start loads one at a time with the largest motor first, and compare your total with the rated watts. Our generator sizing guide explains how.

3. Blocked fuel cap vent

Signs: runs 10 to 30 minutes, then slows and dies; starts again after a rest; sometimes a hiss when you open the cap.

As fuel is drawn out of the tank, air must get in. A blocked vent creates a vacuum that starves the carburetor. Test by running the generator with the cap loosened slightly. If it then runs normally, clean or replace the cap, or open the vent lever if it has one.

4. Carbon monoxide shutoff

Signs: stops after some minutes, usually with a red or flashing CO warning light on the panel.

Newer generators have a sensor that stops the engine when exhaust accumulates around it. It is doing its job. Move the generator to open air, at least 20 feet from buildings and away from walls, fences and vehicles that trap exhaust, and point the exhaust downwind. If it trips in genuinely open air, the sensor may be faulty; contact the manufacturer rather than disabling it.

5. Stale fuel or water in the fuel

Signs: surging, uneven running, popping, then stalling. Often starts easily on choke.

Old gasoline loses the components that make it burn evenly, and ethanol fuel can absorb water that then sits at the bottom of the tank. Drain the tank and the carburetor bowl, refill with fresh fuel, and consider a fuel stabilizer for storage. See how long gasoline lasts.

6. Dirty carburetor

Signs: only runs with the choke partly on, surges at idle, dies when a load is applied.

Varnish from old fuel narrows the main jet so the engine runs lean. Choke richens the mixture enough to run. Remove the bowl and clean the jet and passages with carburetor cleaner, or fit a replacement carburetor, which on many small generators costs little. Then keep the fuel fresh.

7. Clogged fuel filter or sediment cup

Signs: fine at light load, dies under load, runs longer after a rest.

A partly blocked filter passes enough fuel for idle but not for full power. Clean the sediment cup or replace the inline filter and check the fuel line for kinks.

8. Overheating

Signs: runs 20 to 60 minutes, loses power, dies; very hot to the touch; may restart after cooling.

Air-cooled engines need clear cooling fins and an open flow of air. Clean grass, dust and oil from the fins and shroud, make sure the generator is not boxed in by walls or a cover, and avoid running it at full load in direct sun on a hot day. A lean mixture from a dirty carburetor also raises temperatures.

9. Clogged spark arrestor or exhaust

Signs: gradual loss of power, dies under load, sometimes a glowing muffler at night.

The spark arrestor screen in the muffler collects carbon. Remove it (when cold) and clean it with a wire brush, and check that the muffler is not blocked by a mud-dauber nest or debris after storage.

10. Ignition and electrical faults

Signs: dies only when hot and restarts after cooling; or engine runs fine but the outlets go dead.

An ignition coil that fails when hot is a classic cause of heat-related stalling. If the engine runs but the power stops, the problem is in the alternator side: a tripped breaker, a failed capacitor or voltage regulator, or a loose connection. Alternator faults are usually shop work.

Propane and dual-fuel models

A propane generator that dies after a while may have an empty cylinder, a regulator that has frozen, or an excess-flow valve that has tripped because the cylinder valve was opened too quickly. Close the valve, wait a minute, reconnect, and open the valve slowly. In cold weather, small cylinders cannot supply vapor fast enough under heavy load, which also causes stalling. Our guide to dual-fuel generators covers propane behavior in the cold.

Preventing shutdowns

• Check the oil before every run and top it up during long outages.
• Keep fuel fresh or stabilized, and run the carburetor dry before storage.
• Clean the air filter, cooling fins and spark arrestor every season.
• Add loads one at a time and stay within the running-watts rating.
• Give the generator open air on all sides.

The generator maintenance checklist puts these on a schedule, and if the problem is that it will not start at all, see generator won’t start.

Frequently asked questions