Should you repair or replace your standby generator?
Updated August 2026
← Every repair-or-replace call
Keep repairing a standby generator until it passes roughly 12 years or 2,000 run hours; replace it when the engine burns oil, the controller is obsolete, or a quote tops half the $5,000–12,000 an air-cooled unit costs installed. The parts that actually fail on these machines are cheap by comparison. A starting battery is $150–300, a control board or transfer-switch relay $400–1,500, and a valve adjustment a few hundred more, all easy to justify on a machine with a 15–25 year service life. What ends a standby generator is the engine itself, never the accessories bolted around it.
The short version
Count hours before birthdays. A generator that has spent 12 years doing nothing but a weekly exercise cycle may carry only 200 hours and plenty of engine, while a unit in an outage-prone county can burn 2,000 hours in half that time. Under 12 years and under about 2,000 hours, repair almost anything, because batteries, controllers, starters, transfer-switch contacts, and valve lash are all normal service items. Past those marks, apply the 50% rule against a $5,000–12,000 replacement and add one modern wrinkle: if the controller is discontinued and parts sit on backorder for weeks, the machine has already failed at its only job, which is being ready.
Your situation, decided
| Situation | Verdict | Why |
|---|---|---|
| Will not start, battery is 3 or more years old | Repair | A $150–300 battery is the most common no-start cause |
| Under 12 years, controller or transfer-switch relay failed | Repair | A $400–1,500 part on a unit with years of service left |
| Burning oil or losing compression past 2,000 hours | Replace | The engine is worn; the accessories are not the problem |
| Controller discontinued, parts on a 6-week backorder | Replace | A backup that cannot be fixed fast is not backup |
| Past 15 years, quote over half a $5,000–12,000 unit | Replace | The 50% rule on a machine near the end of its life |
| Runs but will not transfer load, switch contacts pitted | Repair | A $500–1,500 transfer-switch repair, not a new generator |
What each path costs
Repairs typically run $150–1,500; a replacement is $5,000–12,000 installed. Standby generators last 15–25 years or 2,000–3,000 run hours, whichever arrives first. Past 12 years or 2,000 hours, weigh any large repair against a new unit. Price your own number on the home maintenance cost calculator before you commit either way.
The repair-or-replace call is easy when you know the unit's age and service history. OnOtto keeps both, plus the maintenance that delays this decision for years.
Start your home's service log, freeFrequently asked questions
How many run hours is too many for a standby generator?
Air-cooled standby units sit near the end of their service life around 2,000–3,000 hours, and liquid-cooled models go further. Most homes never approach that from outages alone, since the weekly exercise cycle adds only 10–20 hours a year. Where the grid drops for days at a time, hours pile up fast and the engine, not the calendar, decides. Read the hour meter on the controller display, then compare it against the 15–25 year lifespan to see which limit your unit reaches first.
My generator did not start during an outage. What failed?
Start with the battery, the single most common no-start cause on standby units and good for only 3–5 years. After that, look at a closed fuel valve, stale fuel on diesel or propane vapor issues, a controller left in manual, a low-oil switch, and mice chewing wiring inside the enclosure. None of that is replacement territory; expect $150–600. This is why the weekly exercise cycle matters so much, because a generator that runs every week warns you about the battery long before the storm does.
Is an annual service contract worth paying for?
For most owners, yes. Annual service runs $200–500 and covers oil and filter, plugs, a battery load test, valve lash on some models, and a transfer-switch check. Set that against a $5,000–12,000 replacement, or against a unit that quits during the one outage you bought it for, and the math is not close. If you handle your own oil changes and follow the service schedule yourself, skip the contract. Do not skip the work.