A generator is one of the few pieces of home equipment that sits unused for months and then has to work flawlessly under stress. Without exercise, fuel goes stale, batteries die, lubrication settles, and the carburetor (on portables) gums up. The pattern that surprises people: the generator that hasn't been started since last hurricane season often won't start at the next one. Manufacturers build in self-test cycles on standby units to address this, but those tests don't verify everything, and portable units have no automatic test at all.

Quick schedule by generator type

  • Standby generator (Generac, Kohler, Briggs, Cummins, etc.):
    • Weekly: automatic self-exercise (factory default, often 10 to 20 minutes).
    • Monthly: homeowner check that the unit started, ran, and reported no faults.
    • Yearly: professional service (oil change, filter, spark plug, valve adjustment per the manual).
  • Portable generator:
    • Monthly: start the engine and run under load for 15 to 20 minutes.
    • Quarterly: check oil level; add or change per manual.
    • Yearly: oil change, air filter check, spark plug check.
    • Annually before peak season: full readiness check.
  • Fuel: add stabilizer to any fuel that may sit longer than 3 months. Replace untreated fuel every 3 months.

Why the test matters

Standby generator manufacturers run self-exercise tests to:

  • Keep the battery charged through the alternator.
  • Circulate oil through the engine.
  • Burn off any moisture that's accumulated in the fuel system.
  • Verify the controller and transfer switch logic.
  • Catch warning codes early.

What self-exercise doesn't always test:

  • The transfer switch transferring power to the home (some units exercise without load).
  • The full load capacity of the generator.
  • Sensors and limits that only trigger under real load.

This is why the monthly homeowner check and the yearly professional service still matter even on a unit that exercises itself.

What the monthly check looks like (standby)

  1. Look at the generator's status light or display. Green/no alarm = normal.
  2. If your unit has an app (Generac Mobile Link, Kohler OnCue), check the last exercise log.
  3. Confirm the exercise ran on schedule and reported no faults.
  4. Walk around the unit. Look for debris, animal damage, or any visible issues.
  5. Check the air intake and exhaust are clear of leaves, snow, or nests.
  6. If there's any concern, run a manual test: press the test button on the controller, listen for normal start-up, confirm the transfer switch operates (you should hear the click, lights blink for a moment as they switch over).
  7. Write the date in your maintenance log.

What the monthly check looks like (portable)

  1. Move the generator outdoors to a well-ventilated area, at least 20 feet from the house, exhaust pointing away.
  2. Check the oil level (cold engine).
  3. Check fuel level. Top off if needed.
  4. Open the fuel valve.
  5. Set choke if cold; engage the recoil or electric start.
  6. Let it run for 15 to 20 minutes.
  7. For a true test, plug in something that draws meaningful current (a space heater or a couple of household appliances). Running with no load doesn't fully exercise the generator.
  8. Listen for normal operation. Watch for smoke, leaks, or unusual sounds.
  9. Shut down per manufacturer (often: remove load, idle for 1 to 2 minutes, kill switch).
  10. Turn off the fuel valve.
  11. Let it cool fully before storing.
  12. Log the test date and any observations.

Fuel handling

Stale gasoline is the #1 cause of generators that won't start when needed.

  • Gasoline without stabilizer starts to degrade in 30 days. By 3 to 6 months, it can be unusable.
  • Use fuel stabilizer (Sta-Bil, Star Tron, etc.) on any fuel that will sit longer than a month.
  • For portable generators: rotate fuel by running through it during monthly tests.
  • For standby generators on natural gas: no fuel concern (gas is delivered fresh from the utility line).
  • For standby generators on propane: tank fuel doesn't go stale, but the system needs to test the regulator.
  • For standby generators on diesel: diesel can also degrade; biocide and stabilizer needed for long storage.
  • Never store gasoline in the house or attached garage. Detached shed or proper outdoor storage cabinet.

Critical safety: CO and electrical

Generator carbon monoxide kills people every year, especially during outages.

  • Never operate a portable generator indoors, in a garage (even with the door open), or within 20 feet of the home with exhaust pointing toward the house.
  • Confirm working CO alarms inside the home before any extended generator use.
  • Don't backfeed power into the house through an outlet. Use a properly installed transfer switch or interlock kit.
  • Don't run a generator under a deck, overhang, or in a tent.
  • Position the generator on a flat, dry surface.
  • Use only outdoor-rated extension cords properly sized for the load.

These are critical-safety rules we don't write workarounds for. Read the manufacturer manual and follow it exactly. See CO detector vs smoke alarm.

What yearly service includes

  • Oil and oil filter change.
  • Air filter check or replacement.
  • Spark plug inspection (and replacement on the manufacturer's schedule).
  • Valve clearance check (varies by manufacturer).
  • Battery check (standby units have a starting battery that fails on 3 to 5 year cycle).
  • Transfer switch operation under load.
  • Fuel system inspection.
  • Coolant check (liquid-cooled standby units only).
  • Update firmware if applicable.

Most manufacturer warranties require documented annual service. Skipping it can void coverage on a $5,000 to $15,000 piece of equipment.

Signs the generator needs attention

  • Self-exercise didn't run on schedule (check the log).
  • Fault code on the display.
  • Unusual sounds during exercise.
  • Smoke from exhaust beyond initial start-up.
  • Engine struggles to start.
  • Battery age over 3 years without replacement.
  • Visible damage, rust, or oil leaks on the unit.

Common mistakes

  • Assuming the standby unit's self-test is enough. It checks engine and battery but not always the full transfer-switch loop.
  • Leaving gasoline in a portable generator for 6+ months without stabilizer.
  • Never running the portable under load, so the fuel system stays gummed up.
  • Backfeeding through an outlet instead of using a transfer switch.
  • Skipping annual service to save money. Voids warranty and shortens unit life.
  • Storing a portable generator outdoors uncovered. Weather damages controls and electrical.
  • Running indoors or near the house during an outage. Kills people.

Good maintenance rhythm

  • Weekly (standby): automatic self-exercise runs.
  • Monthly: homeowner check of standby status; portable run-up under load.
  • Quarterly: visual inspection of generator area, clear debris.
  • Yearly: professional service per the manufacturer.
  • Yearly: confirm CO alarms in the home are operational and within service life.
  • Before storm season (May-June Atlantic, Nov-Jan winter storm): full readiness check.
  • Every 3 to 5 years: replace the starting battery on standby units.
  • For portables: rotate fuel through use; treat any stored fuel with stabilizer.
Add reminders to the Dome mobile app to always stay ahead of your home maintenance.

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