Why Your Boat’s Generator Isn’t Running

If your vessel's genset isn’t running, you’ll have to do some detective work before you can start repairs.

Trolling yacht
The most likely reason for a generator problem is a lack of use, so spend more time aboard your boat and both you and your generator will be happy. Courtesy Lenny Rudow

A boat generator is just like the engines that provide propulsion, but instead of spinning a propeller they spin an alternator to generate electrical current. When something goes wrong in the system, you’ll first need to diagnose the problem and then initiate repairs. Most generator problems fall into one of four categories:

· The generator appears to run fine, but doesn’t produce electricity

· The generator doesn’t turn over


· The generator turns over, but won’t start

· The generator runs, but it runs poorly

Generator Appears to Run Fine but Doesn’t Produce Electricity

First, eliminate the obvious stuff like making sure you’ve flipped the proper switches and checked the breakers. What the issue is will depend, in part, on the type of generator you have. Many marine generators maintain a residual magnetism after they’re powered down, but if they sit for extended periods of time or operate for too long without load, they can lose it. If a generator has lost its residual magnetism it can be restored by “flashing” it with a 12-volt battery. Your owner’s manual may explain the process for your specific generator model, but if not, it’s probably time to call a pro. As a preventive measure in the future, make sure you run your genset under load on a regular basis.


In other scenarios, there could be a bad capacitor. In this case, you may (or may not) detect a burning smell, and you can check the capacitor, as per the manufacturer’s instructions with a multimeter. Other potential suspects include the voltage regulator and control board. Diagnosing these can be difficult, and this task is best left to a professional.

Boat generator
Your boat’s generator is a critical component in producing power on board, so making sure it’s running smooth is a must. Courtesy Lenny Rudow

Generator Does Not Turn Over

In this situation, assuming that you’ve already checked breakers and switches, and that power’s getting to the generator, you’re likely dealing with a switch, solenoid, relay or starter problem. It could also be a wiring connection issue anywhere throughout this system. The gremlin can usually be chased down just as you would with any type of engine that won’t turn, by testing for voltage at one junction after the next until the problem is located.

Generator Turns but Won’t Start

This is another case where generator type will dictate the diagnostic procedures. If it’s a gasoline generator, you need to start by checking fuel, air and spark. If it’s a diesel generator, scratch spark off the list and then look at fuel and air.


Along with chasing down these basic systems, on some older gasoline generators the chokes were prone to getting stuck. Solenoid switches can get stuck, too, and prevent fuel from passing through. On some newer generators, sensors designed to prevent damage during extended use (such as an oil level or high temperature sensor) can also prevent the engine from starting.

As you check these issues, bear in mind that fuel problems are the most common reason a cranking generator won’t start. Checking filters, fuel lines and in the case of diesel units, bleeding the lines and looking for bubbles, should be your initial starting points.

Fuel filter
As with just about any engine, fuel filters are a common suspect when generators won’t run. Courtesy Lenny Rudow

The Generator Runs But Runs Poorly

Like any other engine-driven machine, generators require regular maintenance to keep them running smoothly. When they run poorly, it’s usually due to a lack of maintenance, bad fuel or old age (often in the form of worn out injectors). In any case, your suspects and thus the troubleshooting routine remain the same as for a generator that won’t start in the first place. In many cases, you’ll ID a problem in its beginning stages, such as a partially clogged fuel filter, and head off the inability to start it. But in this case, you should also suspect the fuel itself. If it’s a gasoline generator and you fill up with fuel containing ethanol, the same fuel deterioration issues that affect other engines can cause rough running in a generator, too. If the generator’s fuel tank has gone for a month or more between fill-up with fresh gas, the fuel supply should be the initial item to consider. In the case of diesel generators, fuel contamination (more commonly from microbe growth) can be a problem as well.


The Biggest Reason Your Boat Generator Isn’t Running

Reliable as they are, marine generators are just like any other engine. And like most engines, they need to be run. The most likely reason you’ll have problems with a generator on your boat is simply a lack of use. In fact, a well-maintained five-year-old generator with 1,000 hours of running time on it is less likely to have a problem than one of the exact same age, with 100 hours of running time. The good news? That’s just one more reason why you should be spending more time on your boat.


More Yachts