Standby Generator Troubleshooting: What to Check Before Calling a Pro

Stop: three situations where you should not troubleshoot yourself

Before you touch anything, check for three conditions that require a professional, not a homeowner inspection.

You smell gas or propane. Do not press any panel buttons, do not open the generator access cover, do not attempt any electrical checks. Leave the immediate area, turn off the main propane or natural gas shutoff valve if it is safely reachable without approaching the generator, and call your gas utility.

The generator displays a carbon monoxide fault or alarm. Generators with CO sensors are designed to shut down automatically when carbon monoxide reaches a dangerous level. Do not reset the unit and do not re-enter the area around it. CO is odorless and is lethal at elevated concentrations. Call your installer.

The generator or the area around it has been flooded. Do not attempt to start the unit and do not make any internal inspections. Water in and around electrical equipment is a serious safety risk. Call your installer or a licensed electrician before doing anything else.

If none of the above apply, the checks below are safe for a homeowner to perform.

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Generator won't start during a power outage

This is the most time-sensitive scenario. Most standby generator "failures" during real outages are one of four simple conditions. Check them in order. Each takes less than 60 seconds.

1. Check the control panel mode. Your generator's control panel has a selector switch or mode button that sets its operating state. On Generac models, the options are OFF, MANUAL, and AUTO. For automatic startup during a utility outage, the panel must be set to AUTO. If the switch is in OFF or MANUAL, the generator will not respond to a power failure. Turn it to AUTO.

2. Look for an active alarm or hold state. Some controllers display a HOLD or WAITING status when the generator senses utility power has returned but is waiting to confirm stable voltage before transferring back. This is normal behavior. Wait 30 seconds, confirm the panel is in AUTO, and check again.

3. Check the battery voltage. Most Generac and Kohler residential panels display battery voltage on the status screen. A reading below 12.4 volts at rest, or below roughly 11 volts while cranking, indicates a weak or dead battery. A battery more than three years old that has never been replaced is the single most common reason a standby generator fails to start during a real outage. If the BATTERY or LOW BATTERY indicator is illuminated, battery replacement by a service technician is the fix.

4. Check the fuel supply. For propane units: go to the propane tank and confirm the main shutoff valve is in the open position (handle parallel to the pipe). It may have been accidentally closed during a recent delivery or maintenance visit. For natural gas: confirm your gas service is on by checking another appliance (stove burner, water heater pilot). A gas service interruption during the same event that caused the power outage is uncommon but possible.

5. Check for a recorded fault. If the panel's ALARM LED is lit or the status screen shows an alarm code, the generator has recorded a fault that is preventing restart. Note the code (see "Generator runs but throws a fault alarm" below) before attempting any reset.

If none of these five checks identifies the cause, do not repeatedly try to restart the generator. Call your installer or a licensed service technician with the panel reading in hand.

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Generator starts but the house has no power

When the generator runs and sounds normal but your circuits remain dark, the issue is usually in the Automatic Transfer Switch (ATS), not the generator itself.

Check the ATS status indicator. The transfer switch (usually a gray panel mounted near your main electrical panel) has indicator lights or a status display. A normal state shows a green LED or the word GENERATOR on the display. A fault indicator or a MANUAL position means the switch did not transfer automatically.

Check whether the ATS manual bypass lever is engaged. Transfer switches have a manual bypass position used by service technicians during maintenance. If this lever was left in the bypass or manual position after a service visit, utility power goes directly to your panel but the generator does not connect automatically. Consult your owner's manual for the correct lever position indicator. If you are unsure, do not move it. Call your installer.

Check the generator's main circuit breaker. The generator has its own circuit breaker, typically located on or near the generator enclosure. If this breaker has tripped (handle in the middle or OFF position), the generator is producing power but it is not reaching the ATS or your panel. Reset the breaker once. If it immediately trips again, there is an overload or wiring fault. Call your installer before resetting it a second time.

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Generator starts and then shuts down within seconds or minutes

A generator that shuts itself off shortly after starting is exercising a built-in safety protection. Three causes are common.

Low oil pressure or insufficient oil level. All residential standby generators have an automatic low-oil shutdown. If oil is below the minimum mark on the dipstick, or if oil pressure drops during operation, the engine shuts down and the panel lights an alarm. Check the oil level using the dipstick with the unit stopped and the generator on level ground. If the oil is below the ADD mark, add the grade specified in your owner's manual. Do not attempt to run the generator with confirmed low oil.

Electrical overload. If the total draw from your connected appliances exceeds the generator's rated capacity, its circuit breaker trips or an overload protection circuit shuts it down. During an outage, turn off large loads you can do without: electric water heater, electric dryer, electric range, and EV charger. Then try restarting. If the generator runs stably with a reduced load, you will need a service call to assess whether your load profile matches the generator's capacity.

Overheating. If the exhaust outlet is blocked by debris, vegetation, or snow accumulation, or if clearances around the unit are inadequate, the thermal sensor can trigger a shutdown. With the unit stopped, visually inspect the area around the generator from a safe distance and clear any obstruction from the exhaust and ventilation openings. See generator placement requirements for the minimum clearances around the unit.

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Generator runs but throws a fault alarm

Most residential generators provide a way for homeowners to identify the specific fault without opening the unit.

Generac Evolution and Nexus controllers use LED blink codes. The alarm and status LEDs blink in a specific pattern that encodes the fault number. Count the blinks in the pattern, note the number, and look it up in the troubleshooting section of your owner's manual. Common codes include battery voltage alerts, low oil pressure events, and maintenance reminders. You can relay the exact code to your service technician over the phone for a faster diagnosis before they arrive.

Kohler residential controllers use a plain-text LCD or LED display that shows the fault description directly ("Low Oil Pressure", "Over Crank", "Battery Charger Fault"). Note the exact wording and call your service provider.

What to do with an active fault: For most faults that do not involve gas smell, burning, or CO, it is safe to note the code, set the panel to OFF, and wait for a service technician. Do not repeatedly clear and restart a generator with an active fault. A recurring fault can indicate a condition that worsens with continued operation.

A remote monitoring app such as Generac Mobile Link or Kohler OnCue can send fault alerts to your phone before or during an outage, giving you the fault code without needing to physically inspect the panel.

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Generator passes its weekly self-test but you notice something unusual

Abnormal sounds during operation. A low rhythmic hum and a single brief exhaust pop on startup and shutdown are normal. Sustained grinding, squealing, or rhythmic knocking during operation are not normal. Schedule a service call.

Dark exhaust smoke. A brief puff of dark smoke on a cold startup is normal fuel system behavior. Sustained dark smoke during normal operation indicates a rich fuel mixture or combustion issue. Schedule a service call.

Vibration that feels worse than it used to. Check that the mounting bolts and anti-vibration pads are secure and have not loosened over time. Loose fasteners can often be identified visually. If mounting hardware is secure and vibration is new, the cause is internal. Schedule a service call.

Exercise cycle is completing but the generator shuts down early. Check the controller's exercise timer settings. On many models these can be accidentally changed. If the settings look correct and the unit still shuts down before completing a full exercise, note any displayed fault code and call your installer.

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When to call your installer right away

Stop all troubleshooting and call your service provider if any of the following are true.

• You smell gas or propane near the generator at any point.
• You smell burning or see smoke from the unit.
• You see sparks or arcing from any part of the generator or transfer switch.
• The unit displays or sounds a carbon monoxide alarm.
• The generator has been flooded.
• The unit will not start after two restart attempts following a clean reset (OFF, wait 30 seconds, AUTO).
• The ATS shows a fault after being reset once.
• The main circuit breaker on the generator trips a second time.
• The generator ran for an extended period on low oil before the shutdown occurred.
• The fault code involves "over speed," "over crank," or "governor fault." These conditions can worsen rapidly if operation is reattempted.

For routine servicing, the maintenance schedule guide covers the intervals and service items your installer should handle each year.

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Frequently asked questions

Can I reset a generator fault alarm myself? On most models, pressing OFF and then returning the panel to AUTO clears the active fault and allows a restart attempt. This is safe for advisory or informational faults such as a maintenance reminder or battery voltage notice. Never reset and restart a generator after a safety shutdown due to low oil pressure, over-temperature, or a fuel fault without first addressing the underlying cause.

How many times should I try to restart a generator that won't start? Limit restart attempts to two if you have not identified and resolved a specific cause. Repeated cranking without starting can flood the engine with fuel, which turns a simple fix into a more costly repair.

My generator just ran for 12 hours straight during a long outage. Is that normal? Yes. Residential standby generators are rated for continuous operation. The most important things to monitor during extended runs are oil level (check every 8 hours on a running generator per most manufacturers) and adequate clearance around the unit. Do not attempt to check oil or make any other adjustments while the generator is running unless your owner's manual explicitly describes a procedure for doing so while running.

The generator has not run in six months. Should I be worried? The weekly exercise cycle should be keeping the unit ready even during periods when you do not use it manually. Verify that the battery voltage reads above 12.4V on the panel display and that the exercise cycle log shows recent completions. If you cannot confirm the unit exercised successfully in the past month, a service inspection is a good investment before the next storm season.