How often should a standby generator be serviced?

Short answer

Service the standby generator once a year, or after every 100 to 200 hours of run time, whichever comes first. The service is an oil and filter change, a new air filter and spark plugs as they wear, and a check of the battery, which is replaced every 3 to 5 years. Doing it yourself takes 60 to 90 minutes and $50 to $100 in parts. A service company charges $200 to $400.

Why it matters

A standby generator is a car engine that lives outside, sits idle for months, and is expected to start on the worst night of the year and run for days. Engines don't like that life. Oil breaks down even when it isn't being used. Fuel residue and moisture collect in the carburetor or the injectors. The battery that cranks the engine goes flat sitting in the cold, and the weekly self-test the generator runs is only long enough to keep it from seizing, not to charge a tired battery.

The failure you're guarding against is simple: the power goes out, the generator cranks, and nothing happens. Every part of the yearly service exists to prevent that. Fresh oil keeps the engine from wearing itself out during a long run. A clean air filter and good plugs let it start on the first crank. A healthy battery is what does the cranking. Skipping the service doesn't save money, it moves the cost to the one night you can't afford it.

When to do it more often

• A long outage: check the oil every day the generator runs, and do a full service once the power is back. Several days of running is more wear than a year of self-tests.
• A generator that's been running a lot in a stormy season: count the hours on its meter and service it at every 100 to 200 hours, even if the year isn't up.
• A battery older than 3 years: test it at every service and replace it on the 3 to 5 year schedule without waiting for it to fail.

What you need

• A socket set, for the drain plug and the plug wrench
• An oil drain pan
• A funnel
• Engine oil of the grade the manual specifies
• An oil filter, an air filter and spark plugs for the model, often sold together as a maintenance kit
• A replacement battery when the old one is due

Steps at a glance

1. Set the generator's controller to off, then switch off the utility and battery disconnects as the manual directs.
2. Run the engine for a few minutes first if it's cold, so the oil drains fully, then shut it off and drain the oil into the pan.
3. Replace the oil filter and refill with fresh oil to the mark on the dipstick.
4. Swap the air filter, and the spark plugs if they're due.
5. Check the battery's terminals for corrosion and its voltage, and replace it if it's weak or past 3 years.
6. Look over the enclosure for nests, leaves and rodent damage to the wiring, and clear the air intake and exhaust.
7. Restore the disconnects, set the controller to auto, and run a manual test to confirm it starts and takes the load.

You're done when the generator starts on its own, runs smoothly, transfers the load, and the controller shows no faults.

Signs it's overdue

• A failed weekly self-test, which the controller records and often shows with a warning light.
• Error codes on the controller's display.
• The generator won't start, or cranks longer than it used to.
• Low oil on the dipstick between services.
• A battery older than 3 years, or one that's needed jump-starting.

DIY or pro

This is a moderate job for anyone who has changed the oil in a mower or a car. The engine is a small one, the parts come in a kit for the model, and the manual lays out the sequence. The parts of the job that need care are the disconnects, which the manual is firm about, and the spark plugs, which need the right gap.

A service company charges $200 to $400 for a yearly visit, and the better ones also check the transfer switch, update the controller's firmware, and load test the generator under real demand, which is hard to do yourself. If the generator is under warranty, the maker may require a professional service to keep it. For many owners the right answer is a professional visit every year and an oil check themselves after any long run.

Safety

• Gas: the generator runs on natural gas or propane, and the fuel line stays pressurized when the unit is off. Don't open any fuel connection. If you smell gas around the enclosure, shut off the fuel valve and call the supplier before anyone works on it. Keep the exhaust clear and far from windows and doors, because the engine produces carbon monoxide.
• Electricity: the generator can start on its own at any time when its controller is in auto, and the transfer switch connects it to the house wiring. Set the controller to off and pull the battery and utility disconnects before you touch the engine, and leave the transfer switch and the house wiring to an electrician.

FAQ

How often should I change the oil in a standby generator?

Once a year, or after every 100 to 200 hours of running, whichever comes first. After a long outage, change it as soon as the power is back.

Why does my generator fail its weekly self-test?

A weak battery is the usual reason, followed by low oil, old fuel in the line, or a fault the controller is reporting. The controller's display usually says which.

How long does a standby generator battery last?

About 3 to 5 years. Replace it on that schedule, since a battery that's failing may still pass a short self-test and then fail on a cold night.

Does a standby generator need professional service?

It needs the yearly service done well. Many owners do it themselves, and a professional visit adds a load test and a transfer switch check that are hard to do at home.