The machine has one job, on one night

What is generator maintenance?

Generator maintenance is a scheduled service on an engine that hardly ever runs: oil and filters, spark plugs, the air intake, the battery and charging system, the fuel supply, the enclosure, and a live test through the transfer switch. It follows the manufacturer's stated schedule, which counts both elapsed time and running hours - so a machine that idled through a quiet year is still due. The item that most often stops a standby generator starting is the battery, not the engine.

Signs you need generator maintenance

• You have a standby generator and cannot remember the last time anyone serviced it
• The weekly exercise cycle has stopped happening, or you have never actually heard it run
• A warning light or a fault code is showing on the controller and the machine is otherwise sitting quietly
• It ran roughly during the last outage, or dropped the load when something large started
• You inherited the generator with the house and have no service history for it
• Storm season is approaching and you want to know the machine works before you need it to

Seeing something not on this list? Browse backup generators problems by symptom →

How generator maintenance actually works

1. 1

   Read the controller and the run history first

   A competent visit starts at the controller, not with a spanner. Modern units log run hours, exercise cycles, faults and start attempts, and that history tells the technician what to look at - a machine that has been silently failing its weekly self-test for months is a different job from one that has been running cleanly.

   Watch forA technician who goes straight to the oil without looking at the log. The history is the diagnosis, and it is free.

2. 2

   Test the battery and the charging system properly

   This is the highest-value part of the visit. A standby generator sits with its battery on a maintenance charger for months on end, and the failure mode is a battery that reads a healthy voltage at rest and collapses the moment the starter draws on it. It needs a load test, and the charger itself needs checking, because a failed charger kills batteries quietly.

   Watch forA battery checked with a voltmeter alone and declared fine. Resting voltage tells you almost nothing about whether it can turn an engine on a cold night.

3. 3

   Oil, filters, plugs and the air intake, to the manufacturer schedule

   The consumables, changed on the interval the manufacturer states for that machine - which is defined by both time and running hours, whichever comes first. Air intakes matter more than people expect on an outdoor machine, because they collect grass clippings, leaves, dust and insect nests over a year of sitting still.

   Watch forA service done to a generic annual checklist rather than to the machine's own schedule. Different units and different fuels have genuinely different requirements, and the manual is the authority.

4. 4

   Check the fuel supply under load, not at rest

   On a natural gas machine that means confirming supply pressure while the generator is running and loaded, since a marginal supply looks perfectly fine at idle. On propane it means the tank level, the regulator and the lines. Fuel supply problems are invisible until the machine is asked to work.

   Watch forA pressure reading taken with the machine idle. It is the single most common way a genuine supply problem passes a service visit.

5. 5

   Run a real transfer test and confirm the exercise schedule

   The visit should end with the machine starting, taking real load through the transfer switch, and returning to utility power - the same sequence it will perform in an outage. Then the exercise schedule is confirmed as set and running, at a time that suits you rather than at seven on a Sunday morning.

   Watch forA test run with no load transfer. An engine that starts and runs unloaded has proved one third of the system.

What does generator maintenance cost?

An annual service visit is typically a few hundred dollars, with multi-year or twice-yearly plans priced above that and parts sometimes billed separately. Battery replacement is the recurring extra. Budget for it as a running cost of ownership. See the generator cost guide for ranges.

See the full generator maintenance cost guide - by material, size and region →

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