What a Generator Inspection Should Actually Include
A standard home inspection does not always include the standby generator. Many inspectors note its presence and move on. If a generator is on the property and the seller is asking you to value the home with it included, you want a real evaluation. That means more than a visual.
The inspector should start the unit through a manual transfer or self-test cycle, observe it run under load if possible, and document any warning codes on the controller display. According to the National Fire Protection Association standards for stationary engine generators, regular testing and observation under load are the only ways to confirm a unit will perform when called upon.
Visual Exterior Check
Start with the enclosure. Look for rust streaks, cracked composite panels, mouse droppings around the air intakes, and corrosion on the louvers. The pad itself should be level and not settling. I have seen units rock visibly when running because the pad cracked.
Open the access door if you can do so safely. Check the data plate for the manufacture date. A unit older than 12 years on natural gas is approaching the end of its useful life. Diesel units can run longer with proper maintenance.
Test the Transfer Switch First
The automatic transfer switch is the single most expensive component on the system and the part most likely to fail. It is what disconnects you from the utility and reconnects you to generator power when the grid drops. If it does not work, the generator cannot do anything.
The switch is usually mounted near the main electrical panel inside the house or in the garage. It looks like a gray or black box about 18 inches tall with a manual override handle. The inspector should manually transfer the load to confirm the contacts close properly. Burned or pitted contacts mean a replacement is coming, usually $1,800 to $3,200 installed.
Fuel Source and Supply
Three fuel sources are common: natural gas, propane, and diesel. Each has different inspection points and different long-term cost implications.
Natural Gas
Natural gas units are the easiest to live with because the fuel supply is essentially unlimited. The inspector should verify the gas line is properly sized. A 22kW generator typically needs a 1-inch line at minimum. Undersized lines cause pressure drops that prevent the unit from running at full load.
Check the sediment trap, drip leg, and shutoff valve at the unit. The shutoff should be accessible without tools. Soap-test the connections for leaks.
Propane
Propane units run off tanks that range from 250 to 1,000 gallons. The tank needs annual inspection per the International Fuel Gas Code and many states have additional requirements. Look at the tank gauge, the regulator, and the date stamps on the relief valves. Relief valves expire every 10 years.
Tanks should be a minimum of 10 feet from the building and 5 feet from a property line in most jurisdictions. Local rules vary.
Diesel
Diesel is the rarest choice for residential standby because of fuel storage and rotation requirements. Diesel fuel goes bad in 6 to 12 months without treatment. Look for fuel polishing systems, water separators, and clean tank gauges. If the tank gauge does not move when you press the test button, the sender is bad.
Battery, Oil, and Service History
The starting battery is the second most common failure point. A weak battery prevents the generator from starting when the grid drops. Pull the cover and check the battery date code. Anything older than four years is on borrowed time.
Pull the oil dipstick. The oil should be clean amber to light brown. Black, gritty, or smelling burnt means the unit was run hard without service. Generators need oil changes after the first 25 hours and then every 100-200 operating hours or annually, whichever comes first.
Ask the seller for the service log. A properly maintained unit will have records showing annual service by an authorized dealer. The U.S. Department of Energy publishes general guidance on backup power maintenance that aligns with what most manufacturers recommend.
Run It Under Load
If the unit has not been started recently, ask for permission to do a self-test cycle. Most units have a button on the controller. Listen for irregular cycling, hunting (where the engine surges up and down), excessive smoke, or alarm codes on the display.
A healthy unit settles into a smooth idle within 15 seconds and holds steady RPM. If the controller display shows any active fault codes or service-due indicators, write them down. These cost between $200 for a sensor replacement and $4,000 for a control board.
What to Negotiate If Findings Are Significant
If the generator has issues, you have leverage. A generator that needs $2,000 in service to be operational is not delivering $9,000 of value. Request that the seller either perform documented service before closing or provide a credit equal to the estimated repair cost.
For a unit that is more than 12 years old and showing wear, consider asking for a credit toward replacement rather than repair. Marcus Wheeler in Hinsdale ended up getting a $2,800 credit because the unit was 14 years old and the transfer switch had visible contact damage. He used it toward a newer mid-tier unit after closing.