Generac Generator Maintenance: What to Check and When

Generac generator maintenance is simple to keep up with and expensive to skip. A home standby generator can sit for months without running for an outage, and then be asked to start in seconds and carry the house for hours or days. The parts that let it do that, the battery, the oil, the filters, the spark plugs and the transfer switch, wear or age whether the unit runs or not. This guide covers what the generator does on its own, what you can check as the owner, and what a service visit should include.

We sell and install Generac home standby and commercial generators, and we service standby units after the install. The intervals below are deliberately general. The owner's manual for your model sets the actual schedule, and it is the document to follow.

The exercise cycle the unit runs on its own

A Generac home standby generator runs a short exercise cycle on a schedule set in its controller, typically once a week or on the interval you choose. During that cycle the engine starts and runs for a few minutes without taking over the house. It keeps the engine lubricated, charges the battery, and lets the controller check that everything starts the way it should.

The exercise cycle is your first maintenance check. If you hear the unit run at its usual time each week, that is a good sign. If it stops running, or the controller shows a warning afterward, something needs attention before the next outage, not during it.

What owners can check between visits

• The status lights or display on the controller. Learn what ready, warning and fault look like on your model.
• The monitoring app, if your unit has one connected. Generac calls its system Mobile Link.
• The area around the unit. Keep grass, vines, leaves and stored items clear of the enclosure and the air openings.
• The enclosure itself. Look for damage, nests, ants or rodents, which can chew wiring inside.
• Water around the pad after heavy rain, which can point to a drainage problem.
• Any sound or smell during the exercise cycle that is different from usual.

Owners should not open the engine compartment and work on a unit that can start on its own. The generator can start at any moment if the utility power drops or the exercise timer comes up. Service work starts with putting the controller in the off position and following the manual's safety steps, which is one reason most owners leave it to a technician.

What a service visit covers

A maintenance visit on a home standby generator covers the parts that wear and the systems that have to work together in an outage. The exact list depends on the model and its manual, but a complete visit includes the following.

• Oil and oil filter changed, with the right oil for the season and the model.
• Air filter inspected and replaced as needed.
• Spark plugs inspected, gapped or replaced.
• Battery tested under load, terminals cleaned, and the battery replaced when it is weak.
• Controller checked for stored faults and settings, with updates applied where the model supports them.
• Transfer switch tested by simulating an outage, so the house actually moves to generator power and back.
• Wiring, connections and the enclosure inspected for heat, corrosion, insects and rodents.
• Exercise schedule confirmed and the unit returned to automatic.

Our generator service and repair page explains how we handle maintenance visits and repairs on standby units.

Oil, filters and spark plugs

The engine in a home standby generator works like any small engine. The oil breaks down with running hours and with heat, and an outage in July can put many hours on the unit in a few days. The air filter keeps dust out of the engine, and in a dry, windy stretch it can load up faster than the calendar suggests. Spark plugs wear and foul over time, and a worn plug is a common reason an engine is slow to start.

None of these parts is expensive, and all of them are quick to change on a scheduled visit. The cost of skipping them shows up later, as an engine that will not start, runs rough under load, or wears out early. Use the oil grade and the parts the manual names for your model, and keep the receipts with your maintenance log.

The controller and the settings

The controller is the brain of the generator. It runs the exercise schedule, watches the engine while it runs, and stores a record of faults and warnings. On a service visit the technician reads that record, because a fault that cleared itself weeks ago can still point to a part that is starting to fail. The visit also confirms the date and time, the exercise schedule and any settings that affect how the unit starts and stops, and applies updates where the model supports them.

If your unit is connected to a monitoring app, the technician can also check that it is still reporting. A monitoring connection that dropped months ago looks exactly like a generator with nothing to report, and only one of those is good news.

Why the transfer switch test matters

A generator that starts and runs is only half the system. The transfer switch has to sense the outage, signal the generator, wait for it to come up to speed, and move the house over. When utility power comes back, it has to move the house back and let the generator cool down. A visit that runs the engine but never tests the switch has not tested the thing you are counting on.

If you are adding or replacing a switch, our guide to generator transfer switch types covers the types and how they are wired.

How often: follow the owner's manual for your model

Maintenance intervals are set by the manufacturer for each model, usually as a number of running hours or a length of time, whichever comes first. Air-cooled and liquid-cooled units have different schedules, and a unit that ran for days during a long outage may be due sooner than the calendar says. Follow the owner's manual for your model's intervals, and keep a record of every visit. Warranty terms can ask for maintenance records, so a written log is worth keeping in any case.

As a practical rule, plan a full service visit at least once a year, and another after any long outage. In San Antonio, many owners schedule it in spring, before the summer storm season and the heat that puts the most load on the unit.

Texas heat, dust and the battery

Heat is hard on batteries. A battery that tested fine in the winter can be weak by August, and a weak battery is one of the most common reasons a standby generator fails to start. Dust and cottonwood fluff can clog air openings and filters, and fire ants and rodents like the warm, sheltered space inside an enclosure. Each of these is cheap to catch on a maintenance visit and costly to find out about during an outage.

When to call for a repair instead of waiting

• The unit has stopped running its exercise cycle.
• The controller shows a fault or a warning that does not clear.
• The unit started during an outage but the house stayed dark.
• The house stayed on generator power after utility power came back.
• You smell gas near the unit. Leave the area and call the gas utility first.

For how we install Generac units, see our Generac generators page. If you are still choosing a unit, our free in-home generator sizing visit is where we build the load list with you, and our generator installation service covers standby generators in general. If you are comparing brands, see our guide to Generac vs Kohler.