Backup generator problems
Most backup generator failures trace to four things: a dead starting battery, stale or contaminated fuel, skipped maintenance, and a unit that was undersized for the load. Bob Vila's maintenance guidance calls for oil changes roughly every 100 hours of operation, air filter and spark plug service at about a year or 100 hours, and professional service every two years or 200 hours - the intervals people skip are the ones that strand them.
It won't start when the power goes out. On standby units, the usual culprit is the starting battery. That's why the weekly exercise cycle exists - the unit runs itself for a few minutes on a set schedule to keep the battery charged and the oil moving. If you never hear yours run, something is wrong and you should find out now rather than during a storm.
It starts, then quits under load. That's often an undersized generator or too much on the transfer switch. Sizing math is running watts plus the single largest starting surge; central air alone can need roughly 3,000 running watts and about three times that to start. A common rule of thumb is to keep the generator at no more than 90 percent of its rated capacity.
Portable unit won't start after storage. Gasoline left sitting varnishes the carburetor. Bob Vila's guidance is to run a portable every two weeks for five to ten minutes if there's fuel in the tank, and to use a stabilizer for shorter storage periods rather than leaving untreated fuel to sit.
It runs but nothing in the house has power. That's a transfer switch or breaker problem, not an engine problem. It's also the point at which people start improvising dangerous connections. Don't. Call the installer.
Choosing backup generators a fix
The judgement calls that decide the bill, before anyone quotes you.
- Listen for the exercise cycle Standby units typically self-test weekly for several minutes. Note the day and time. Silence for a few weeks is your early warning.
- Treat the battery as a consumable A starting battery is the most common reason a standby generator does nothing during an outage. Ask your service tech to load-test it at every visit.
- Recheck sizing when you add big loads A new heat pump, EV charger or well pump can push you past what the generator can carry. Central AC needs roughly 3,000 running watts and about 9,000 to start.
- Don't store untreated gasoline Stale fuel is the number one reason a portable generator that worked last year won't start this year.
- Distinguish engine faults from switch faults If the engine runs and the house is dark, the problem is downstream. That's a warranty and installer conversation, not a fuel one.
All backup generators problems
Power Outages
No Backup Power
Undersized Generator
Transfer Switch Missing
Fuel Storage Concerns
Quiet Hours Restrictions
Where these figures come from
Sources last checked
- Bob Vila - Generator Maintenance · retrieved 2026-07-26
- Bob Vila - How Big of a Generator Do I Need? · retrieved 2026-07-26
- Bob Vila - How to Choose a Generator · retrieved 2026-07-26
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