Why didn't my standby generator start during a power outage?

When a standby generator sits silent through an outage, one link in a short chain has failed. Either the generator never received the signal to start, it tried to start and could not, or it started but never took over the house. Each points to different causes, and the generator's controller display usually tells you which one you are dealing with. Write down any message exactly before anyone resets anything.

How the start is supposed to happen

The transfer switch is the trigger. "An automatic transfer switch monitors the utility power and signals the generator set to start when utility power is lost."^[1] On Kohler's RXT switch, the utility is treated as failed when its voltage falls below the undervoltage dropout setting, which is 90% of the pickup setting, itself 90% of nominal voltage.^[2] At factory settings, the engine start delay is 3 seconds and the transfer delay after the generator is ready is another 3 seconds.^[2] Generac describes its units coming on within seconds of sensing an outage.^[4] Our answer on how a standby generator connects to a house walks through the whole system.

It never got the signal

The controller was not in AUTO. This is the most common and the simplest. Kohler's controller warns: "The generator set is not in Automatic (standby) mode. Remote start and stop commands from a transfer switch or remote switch will be ignored."^[1] With the controller in OFF, remote start commands have no effect and the weekly exercise will not run.^[1] Generators are often left out of AUTO after a service visit, a manual test or a cleared fault. Returning it to AUTO is an owner setting in your manual; if it keeps dropping out, call for service.

The outage was too short, or only partial. The engine start delay exists to guard against starting the generator because of a brief change in the utility source,^[2] so a flicker shorter than that delay is meant to pass. And because the switch acts on voltage, a sag or partial loss that never drops below its dropout setting still looks like utility power to it. If lights were dim or half the house was dark while the generator stayed off, tell the technician and the utility both.

The switch lost contact with the generator. The transfer switch and generator talk over control wiring. On Kohler systems, an ATS fault indicates that the connection to the interface board on the transfer switch has been lost.^[1] That is wiring work for a licensed electrician or dealer.

It tried but could not start

Kohler's manual starts in the right place: "First check for simple causes such as a dead engine starting battery, loose connections, or an open circuit breaker."^[1]

The battery. The generator cranks on its own battery, and its charger needs house power: Kohler requires that the power to the battery charger must be backed up by the generator.^[3] If the circuit feeding the charger is off, the battery can slowly drain. Kohler's controller raises a low battery warning when the starting battery stays below 12.5 volts for more than 90 seconds with the engine stopped, and a low cranking voltage warning when it falls below 8 volts for more than 6 seconds while the starter is engaged.^[1] The good news is that the controller checks battery voltage before each exercise run,^[1] so a weak battery often shows up as a warning before an outage.

Fuel. For an engine that cranks but will not run, or stops suddenly, Kohler's troubleshooting table lists no fuel and insufficient fuel pressure, each with a check of the fuel valves and supply.^[1] On propane, look at the tank gauge; Kohler's service schedule includes checking the main tank supply level weekly.^[1] On natural gas, notice whether your other gas appliances are working.

It gave up cranking. On Kohler's 20 kW models with controller firmware 1.4.4 or later, the controller makes three starting attempts of 15 seconds cranking and 15 seconds off, pauses 45 seconds, tries three more times, and then shuts down on an overcrank fault.^[1] Overcrank is a symptom; fuel, spark and battery are the usual suspects.

A fault shutdown was already waiting. If the generator shut itself down during an earlier exercise, it will not start until the fault is cleared. On Kohler's controller: "In Auto mode, OFF LED flashes quickly to indicate a fault shutdown."^[1] Kohler's rule is plain: "Always identify and correct the cause of a fault shutdown before resetting the controller."^[1] Low oil pressure is a common one, and Kohler notes that the low oil pressure shutdown is not a low oil level shutdown, so the oil level still needs checking regularly.^[1]

For a fuller list of no-start causes, see why a standby generator won't start.

It started, but the house stayed dark

If you heard the engine running and nothing came on, the problem is between the generator and your panel. For no output, Kohler lists a line circuit breaker in the OFF position, a breaker tripped by overload or a short circuit, and a tripped auxiliary winding breaker.^[1] Its guidance on repeats is direct: "If the generator set circuit breaker trips repeatedly, contact an authorized distributor/ dealer for service."^[1] A transfer switch that failed to move is electrician's work. Kohler's optional status indicator panel for the RXT switch has status LEDs that show whether utility and generator power are available and which source is supplying the building,^[2] which helps the technician see where the chain broke.

What you can safely check

Read the controller display and note every message, the date and how long the power was out. If your unit is connected to Wi-Fi, Generac's Mobile Link app shows a connected generator's operating status.^[4] Check the propane gauge, and whether the controller is in AUTO. Leave the enclosure closed: generators connected to transfer switches will start automatically during exercise periods and power outages,^[1] and Kohler warns: "Accidental starting can cause severe injury or death."^[1]

If you smell gas, Columbia Gas of Virginia tells its customers to "go outside and call 911 and then call us at 1-800-544-5606,"^[5] its 24-hour emergency line. Customers of other gas companies or propane suppliers should use their own emergency number. And because any engine makes carbon monoxide, Ready.gov's advice applies: "Install working carbon monoxide detectors on every level of your home."^[6]

Keeping it from happening again

Most of these failures are caught by routine. "Exercising the generator set weekly or every two weeks is required to keep the engine and alternator in good operating condition."^[1] Regular service catches weak batteries, low oil and fuel problems before a storm. See how often a standby generator needs maintenance.

When to call a licensed pro

Call for any fault you cannot tie to an obvious cause like an empty propane tank, for an overcrank or low oil pressure shutdown, for a battery or charger warning, for a breaker that keeps tripping, and whenever the generator ran but the house did not switch over. Give the technician the exact messages, the model and serial number, and what happened during the outage.

Repairs to the wiring and transfer switch are licensed work. Virginia defines an electrician as a tradesman who works on electrical systems regulated under the Uniform Statewide Building Code,^[7] and Virginia law requires a licence to work as a tradesman, as a liquefied petroleum gas fitter or as a natural gas fitter provider.^[8] Check the licence before work starts.

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If your generator failed you in an outage, describe the problem once and licensed local businesses quote the repair.