Generator Won't Start: Troubleshooting Guide
In This Guide
Few faults are more stressful than a generator won't start situation, and it always seems to happen at the worst possible moment, with the power already out. The good news is that the causes are predictable and most are quick to fix, because a generator that refuses to start is usually suffering from stale fuel rather than anything expensive. Work through these checks in order and you will find the problem the great majority of the time.
Start With the Obvious (Genuinely)
Before anything else, rule out the simple things that catch everyone out. It is not condescending, it is efficient, because these account for a real share of no start calls.
1. Is there fresh fuel?
Not just fuel, fresh fuel. Petrol older than about thirty days may already be degrading.
2. Is the fuel valve open?
Many generators have a fuel shutoff valve. It must be open. This alone stops a surprising number of machines.
3. Is the choke set?
A cold engine needs full choke to start. Once running, it comes back off.
4. Is the engine switch actually on?
There is often both a switch and a key or a separate on/off. All of them need to be in the run position.
Check the Low Oil Shutdown
Nearly every modern generator has a low oil sensor that prevents the engine starting if the oil level is too low. It is a protective feature, and it is a very common reason a generator will not start.
Check the oil on the dipstick. If it is low, top it up to the correct level and try again. Note that some generators are sensitive to being on uneven ground, which can falsely trigger the sensor, so start it on a level surface.
The Real Culprit: A Blocked Carburetor
If the fuel is fresh, the valve is open, the choke is set, and the oil is fine, and it still will not start, you are almost certainly looking at a carburetor blocked with varnish.
This is what stale fuel does. As petrol degrades it leaves a sticky, gummy residue that dries into varnish and seals the tiny passages inside the carburetor, particularly the main jet, which is finer than a pin. Fuel simply cannot get through, so the engine has nothing to burn.
Cleaning the carburetor is the fix, and it resolves the large majority of stubborn no starts. We cover the full process in our generator carburetor cleaning guide.
Electric Start: Check the Battery
If your generator has electric start and nothing happens when you turn the key, the battery is the first suspect. Generator starting batteries sit for long periods and go flat, exactly like the fuel goes stale.
- If you hear a single click or rapid clicking, the battery is likely flat or the connections are corroded.
- Check the battery terminals are clean and tight.
- Most electric start generators also have a recoil pull cord as a backup. If it starts on the cord but not the key, the fault is the battery or starter, not the engine.
Recoil Start: Check the Spark Plug
A fouled, wet, or worn spark plug is a common no start cause on any generator. Remove it and look.
| Plug looks | Meaning |
|---|---|
| Wet with fuel | Engine is flooded, or not firing. Dry it and check for spark. |
| Black and sooty | Running rich, or a dirty air filter. Clean or replace. |
| Dry and pale | Not getting fuel. Points back to the carburetor. |
| Worn or damaged | Replace it. Plugs are cheap. |
Still Nothing? What It Might Be
If you have worked through all of the above and the generator still will not start, the remaining possibilities are fewer and more involved: a failed ignition coil, a clogged fuel line or filter, a stuck float in the carburetor, or a compression problem.
Rather Have a Real Technician Handle It?
A Wildwood technician comes to your home, diagnoses the generator on site, and gets it running, usually in about an hour. More than 10,000 repairs completed since 2019, with flat rates quoted before we arrive so there are no surprises. When you need power back, you need it back now.