Backup generator didn't start: what to check

Most standby generators that fail to start have a simple cause: the controller is not in automatic mode, the battery is weak, fuel is low or shut off, or there is an active alarm. Check those safely, never run a portable generator indoors, and never plug one into a wall outlet. Call 833-877-1717 to request an independent generator or electrical provider.

Am I in the right place?Yes, if a standby or portable generator did not start, shut down, or is not powering the building.

Is this urgent?Urgent when power loss affects medical equipment, refrigeration, heating, cooling, sump pumps or business operations.

What do I do next?Do the safe checks below, keep exhaust outdoors, and call 833-877-1717 for generator repair.

Call 833-877-1717 Generator repair help →

RepairNowUSA Editorial TeamUpdated October 13, 2026Editorial standards

RepairNowUSA editorial review · Last substantively reviewed October 13, 2026 · Review standards

Electrician testing a breaker panel in a garage with a multimeter

Safety first: carbon monoxide and backfeeding

Run portable generators only outdoors, far from doors, windows and vents. Never in a garage, basement or enclosed area, even with doors open.
Make sure CO alarms in the building are working.
Never plug a generator into a wall outlet. "Backfeeding" can energize utility lines and kill line workers. Generators must be connected through a transfer switch or approved interlock.
Let a generator cool before refueling.

Standby generator: the four common causes

Not in auto mode: after maintenance or testing, the controller is often left in "Off" or "Manual". Check the display.
Battery: the starting battery is the most common failure. Corroded terminals or a battery older than its rated life are typical. A battery charger fault may show on the display.
Fuel: natural gas valve closed or utility gas interrupted; propane or diesel tank low; diesel that has gone bad or gelled in cold weather.
Active alarm: low oil, overcrank, overspeed or high temperature alarms lock the unit out. Write down the alarm before you reset anything.

Running but the building has no power

The automatic transfer switch may not have transferred. Check its display or indicator lights.
The generator's output breaker may be tripped.
Only some circuits are on generator power by design. Check which loads are on the emergency panel.
Do not operate a transfer switch manually unless you have been trained on that equipment.

If it started and then shut down

Overload: too many loads came on at once, especially large motors or HVAC.
Low oil or high temperature: check oil level only with the unit off and cool.
Fuel starvation under load.
Blocked air intake or exhaust, including snow or debris around the enclosure.

Protect what matters while you wait

Prioritize life-safety and medical loads. If someone depends on powered medical equipment, have a backup plan and call 911 if their safety is at risk.
Keep refrigerators and freezers closed.
Plan for sump pumps in wet weather.
Turn off sensitive equipment to protect it when power returns.

Maintenance that prevents the next failure

Standby generators need regular exercise runs, periodic load testing, battery replacement on schedule, oil and filter service, and fuel management. Commercial and healthcare facilities often have code-required testing schedules. Keep a log.

When you call 833-877-1717, give the generator brand, size, fuel type and any alarm on the display. RepairNowUSA looks for a participating independent generator or electrical provider; the provider confirms timing and price with you.

How RepairNowUSA can help

Call 833-877-1717 and describe what is happening and the property ZIP code. RepairNowUSA looks for a participating independent provider for that kind of work in your area and connects you if one is available. The provider confirms timing, scope and price with you and does the work. Availability and response times vary and are not guaranteed.

Call 833-877-1717

Common questions

Why did my standby generator not start during the outage?

The most common causes are a controller left out of automatic mode, a weak starting battery, a fuel problem, or an active alarm locking the unit out.

Is it safe to run a portable generator in the garage with the door open?

No. Carbon monoxide can build up to deadly levels in garages and enclosed spaces even with doors open. Run it outdoors, far from openings.

Can I plug my generator into a wall outlet?

No. That backfeeds the building wiring and can energize utility lines, endangering line workers. Use a transfer switch or approved interlock installed by an electrician.

How often should a standby generator be tested?

Manufacturers commonly recommend regular exercise runs and periodic service. Commercial and healthcare facilities may have code-required testing. Follow the manufacturer's schedule and your local requirements.

Can I call any time?

Yes. You can call 833-877-1717 at any time, including nights, weekends and holidays. Whether an independent provider can come out right away depends on your ZIP code, the time and provider capacity, so availability is not guaranteed.

Authoritative references

These public sources give general safety context. They do not replace an on-site evaluation, and RepairNowUSA does not perform the work.