Generac Generator FAQ: Biggest Models, Maintenance Reset, Spark Plugs & More

Frequently Asked Questions About Generac Generators

I've been handling generator orders and installations for about six years now. In that time I've personally screwed up – a lot. Forgot to reset the maintenance light on a 22kW install, ordered the wrong oil filter for a 38kW unit (felt like an idiot), and once tried to test voltage with a regular multimeter probe that wasn't rated for the output. That last one cost me a fried meter and a lecture from my senior tech. So here's what I wish someone had told me upfront – the real answers to the questions people actually ask.

What is the biggest Generac generator?

The largest air-cooled standby generator Generac makes for residential use is the 26kW model. But if you go into the liquid-cooled commercial series, the biggest is the 38kW – which is basically a small building powering an entire house with AC, well pump, and a shop. I installed a 38kW for a customer last year (2024) who kept asking if they could run their whole neighborhood. Short answer: no. But it'll handle a 4,000 sq ft home plus an RV hookup without breaking a sweat. For reference, the 38kW uses a 999cc engine – that's bigger than most car engines. The key takeaway: 26kW air-cooled is the biggest “typical” home model; 38kW liquid-cooled is the heavy-duty option (and requires a concrete pad and propane tank upgrade).

I actually ordered a 26kW for a customer once without checking their load calculation – they had a 5-ton AC unit and a well pump that kicked on simultaneously. The generator couldn't handle the startup surge. That mistake cost me a $1,200 change order and two weeks of delays. Lesson: bigger isn't always better if you don't match the load profile.

How do I reset the maintenance reminder on a Generac generator?

This is probably the most common question I get after installations. The reset procedure is straightforward, but I've seen people mash buttons in frustration for 10 minutes. Here's the exact method for most Generac standby units (model year 2019 and later):

Press and hold the OFF button on the controller for about 5 seconds until the display shows “MAINTENANCE RESET?” Then press the ENTER button to confirm. That's it. On older models (2014-2018), it might be a combination of pressing the MENU button twice and then selecting RESET. I've had a few phone calls where the customer swore it didn't work – turns out they were holding the AUTO button instead of OFF. Total waste of time. (I did that myself on my first install back in 2019 – felt pretty dumb.)

One thing to watch: if you've just changed the oil but haven't run the generator after the service, the reminder might not clear until you cycle the unit. So run it for a minute or two, shut it down, then reset.

How to remove a spark plug on a Generac generator?

Removing the spark plug is simpler than you'd think – but I've seen people try to yank off the boot without twisting, which rips the rubber. Step one: disconnect the spark plug wire by grasping the boot (not the wire itself) and giving it a half-turn while pulling. Then use a 5/8" spark plug socket (or 13/16" for some older models) with a ratchet extension. Most Generac generators have the plug on the side of the engine, accessible after removing the service panel. Turn counterclockwise. That's the whole deal.

Now, here's where I messed up: I once cross-threaded a new plug because I didn't hand-start it first. You need to screw it in by hand for the first few turns to make sure it's aligned. The aluminum threads in the engine block can strip easily – and a stripped thread means a new cylinder head ($$$). So bottom line: hand-thread, then torque to 20-25 lb-ft (check your owner's manual). Also, check the gap – most Generac plugs need 0.030 inch gap. I keep a gapping tool in my truck now after one failed startup from an incorrectly gapped plug.

What type of oil filter does a Generac generator use?

This one confused me for a while because Generac uses different filters depending on engine size. For the popular 22kW and 24kW models (the 999cc V-twin engine), the OEM oil filter part number is 0G6060E. It's a spin-on filter that looks about the size of a soda can. For the smaller 6kW portable units, they often use a cartridge-style filter (p/n 0H0683A). And for the massive 38kW commercial unit, it's a larger spin-on filter (p/n 0J7374B).

I once ordered a filter for a 22kW and accidentally got one for a 38kW – it was too big to fit in the housing. Felt stupid. So here's a tip: cross-reference with your serial number before buying. You can also use aftermarket filters like Wix 57002 or Purolator PL30001 for the 999cc engine, but I stick with OEM for warranty reasons. Also note: the MT 07 oil filter (used on Yamaha motorcycles) is not compatible – different thread pitch. A customer tried to tell me it worked “fine” but it leaked after 10 hours. Don't be that guy.

How to use a high voltage probe for multimeter to test generator output?

Testing generator voltage output requires some care – especially if you're dealing with a 240V standby unit. A standard multimeter probe is rated for maybe 600V max, which is fine for 240V. But the issue is safety and accuracy when measuring across phases. A high voltage probe (rated for 1000V or more) is overkill for residential generators, but if you're using one, here's the right way:

Set your multimeter to AC voltage (V~). Plug the high voltage probe into the meter – usually it has a BNC connector that adapts to the meter's inputs. Set the probe's attenuation ratio (typically 10:1 or 100:1) and make sure the meter compensates for that (some meters have a button to switch between 1:1 and 10:1). Then connect the probe's ground clip to the generator's ground terminal or a known ground. Touch the probe tip to the hot terminal (L1 or L2). Read the voltage on the meter – for a 240V output, you should see 240V ±5% with no load.

I had a scare in 2022 when I touched the probe to L2 while the ground clip wasn't connected – got a mild shock because the meter floated. That taught me to always clip ground first. Also, if you're testing a 38kW commercial unit, the output can be 480V three-phase – in that case, a high voltage probe is absolutely necessary because the phase-to-phase voltage can exceed 600V. Don't try that with a standard probe. I watched a colleague arc-weld his meter once. Not pretty.

Why does my Generac generator shut off after a few seconds?

This isn't in your list but it's so common I have to include it. If your generator starts, runs for 2-5 seconds, then shuts down, it's almost always a low oil pressure or overcrank fault. The controller detects that either oil pressure isn't building or the engine isn't reaching proper RPM. Check the oil level first (I've found units delivered with no oil from the factory – yes, really). Then check the spark plug gap and fuel supply. If it's a propane unit, make sure the tank has enough fuel and the regulator isn't frozen. I once spent 45 minutes troubleshooting a unit that just needed a new battery – the control board was dropping voltage below 11V, causing a false fault. So check battery voltage too.

To be fair, these generators are pretty reliable overall. But the first time you see one crank and die, it's nerve-wracking. I've been there.