Why won't my standby generator start?

Most standby generators that will not start have a simple problem: the controller is not set to start on its own, a fault shutdown is waiting, the starting battery is weak, or fuel is not reaching the engine. Less often it is spark plugs, a clogged air cleaner, low oil pressure, or a failure in the engine or controller. The controller display usually tells you which, and reading it is the most useful thing you can do before you call.

Read the controller first

A standby generator's controller records what went wrong. Look at the display for a fault or warning message and write it down exactly, along with the date and whether the power was out. If your generator is connected to Wi-Fi, the maker's app may show the same thing: Generac's Mobile Link app shows a connected generator's operating status.^[4] A technician who knows the message before arriving can bring the right parts.

The common causes, in order

It is not set to start automatically. On Kohler's controllers, the warning reads: "The RDC2 controller is not in AUTO. The generator will not start from an ATS or remote device."^[2] Kohler's owner's manual lists the generator being in OFF mode as a reason it does not crank, with AUTO as the setting that allows remote starting.^[1] If it keeps dropping out of AUTO, that is a job for a technician.

A fault shutdown is waiting. When a generator shuts itself down to protect the engine, it will not start again until the fault is cleared. Kohler's manual is clear about the order: "Identify and correct the cause of the fault condition. Then reset the controller after a fault shutdown."^[1] Clearing a fault without fixing its cause usually brings it straight back, so leave anything beyond an obvious cause to the technician.

The battery is weak or dead. The generator cranks on its own 12-volt battery, separate from your house power. On Kohler's units, a dark controller display points to low or no battery voltage,^[1] and the first causes listed when the engine will not crank are a weak or dead battery and reversed or poor battery connections.^[1] Kohler's controllers also raise a low cranking voltage warning when battery voltage falls below 60% for 6 seconds or more during cranking.^[2] Batteries usually weaken with age and struggle more in cold weather, and a failing battery charger can let a good battery run down. After a battery is replaced, the exercise schedule may need setting again: "If the battery is disconnected for service or replacement, the exercise settings on the controller are lost."^[3]

Fuel is not getting through. If the engine cranks but does not start, fuel comes first. Kohler's service manual lists an empty propane tank, a closed manual fuel valve, damaged fuel regulators and loose connections at the fuel solenoid valve.^[2] A low propane tank is a call to your supplier, and on natural gas it helps to tell the technician whether your other gas appliances work. A generator that runs briefly and then struggles may not be getting enough gas: Kohler tells technicians to "Verify adequate fuel pressure and pipe size for the generator set plus all other gas appliances,"^[2] since an undersized line or meter can starve it when the furnace and water heater are running too.

It cranks and cranks, then quits. On Kohler's controllers: "If the engine does not start successfully after 3 crank cycles, an Overcrank fault occurs."^[2] Overcrank is a symptom rather than a cause. Fuel, spark and the engine are the usual places to look, and that is the technician's work.

Engine and ignition parts. Further down the lists are a clogged air cleaner, loose spark plug wires and worn spark plugs,^[1] and a low oil pressure shutdown.^[1] Kohler also describes a Locked Rotor shutdown, which means no rotation of the engine or alternator was detected for 3 seconds or more during cranking.^[2] That one points to the starter or a mechanical problem.

A stop switch or overheating. Some units have an emergency stop or engine shutdown switch, and Kohler lists the case where an emergency stop switch or engine shutdown switch has been activated^[1] as a reason the engine will not crank. Some Kohler models also have an enclosure thermostat: "If the thermostat trips, the generator will shut down,"^[1] and Kohler's first check is for blocked air inlets and exhaust outlets.^[1] Leaves, snow, mulch and overgrown shrubs are common culprits. Kohler's installation manual says "No plants, shrubs, or other combustible materials are allowed within 1.2 m (4 ft.) of the exhaust end of the generator set."^[3]

If it runs but the house stays dark

A generator that starts but does not power the house has a different problem, often a tripped generator breaker or a transfer switch fault. Kohler's owner's manual says: "If the generator set circuit breaker trips repeatedly, contact an authorized distributor/ dealer for service."^[1] The transfer switch sits between your panel and the utility, so anything inside it is a job for a licensed electrician.

Stay safe while you wait

Do not open the enclosure or work on the unit while it can start. Generator sets connected to automatic transfer switches start automatically during exercise periods and power outages,^[3] and Kohler warns that "Accidental starting can cause severe injury or death."^[1] Even Kohler's service manual notes that "Corrective action and testing in many cases requires knowledge of electrical systems and electronic circuits."^[2]

If you smell gas near the generator or in the house, Columbia Gas of Virginia tells customers to get out immediately and, from a safe location away from the building, call 911 and its emergency number, 1-800-544-5606.^[5] If you have another gas company or a propane supplier, use its emergency line.

Any engine makes carbon monoxide. Ready.gov's advice: "Install working carbon monoxide detectors on every level of your home."^[6] It warns that "Carbon monoxide is a colorless, odorless gas that can kill you, your family and pets."^[6]

When to call a licensed pro

Call for any fault you cannot trace to an obvious cause such as a low propane tank, for an overcrank, low oil pressure or locked rotor fault, for a battery or charger problem, for a breaker that keeps tripping, and before the next storm if the generator missed its weekly exercise. Give the technician the exact fault message, the model and serial number from the nameplate, and when it last ran.

The repair work is licensed in Virginia. The state defines an electrician as a tradesman who performs the construction, repair, maintenance, alteration, or removal of electrical systems regulated under the Uniform Statewide Building Code,^[7] and a gas fitter's work includes the repair of liquefied petroleum or natural gas piping, tanks, equipment and appliances annexed to real property.^[7] Virginia law requires a licence to work as a tradesman or as a liquefied petroleum gas fitter.^[8] Check the licence before work starts.

If the diagnosis comes back expensive, read whether to repair or replace an old standby generator, and to keep it from happening again, see what a standby generator service visit includes. Browse generator repair, find electricians in Blacksburg, or read more electrical repair answers.

If your generator will not start, describe the job once and licensed local businesses quote the repair.