Generator Cranks but Won’t Start: The No-Code Walkthrough

Last updated: October 2026

It turns over with real conviction — and never catches. No red light yet, or a code you haven’t read. This is the most common standby failure shape there is, and it has a logic: an engine needs fuel, air, and cranking speed, in that order of likelihood. On a Generac, five failed crank attempts turn this symptom into code 1100 (overcrank) — this walkthrough is that code’s sequence, written for the moment before the code sets. The same physics applies to every brand: Cummins Onan calls it Code 4 (Over Crank), and Kohler’s controller logs “Over Crank” after three unsuccessful attempts.

First: read the controller anyway

Before the walk, look at the display. A stored code — even one from last week — outranks symptom-guessing, and “it just won’t start” plus a stored 1505 or 1300 is a completely different (shorter) investigation. If there’s a code, run it through the free diagnostic first. Truly no code? Proceed.

1. The fuel shutoff valve

Ten seconds, $0, and the most common single find: the valve on the fuel line near the unit — and the one at the LP tank — must be fully open. Valves get closed for service, fuel work, even landscaping, and a closed valve produces exactly this symptom on a mechanically perfect machine.

2. Fuel quantity and supply

LP: read the tank gauge. Generac’s guidance is that below about 30% the tank may not sustain pressure for a start — worse in the cold, when a low tank can’t vaporize propane fast enough. Natural gas: check your supplier’s site for outage or construction notices; grid pressure sags during neighborhood-wide events are real, and no wrench in your garage fixes the street’s pressure.

3. Fuel selection (recent install or service? Read this twice)

Generac units ship from the factory set to natural gas. Running on LP requires two things, not one: selecting LP at the controller (or in the Field Pro app on Power Zone 200 models) and orienting the fuel jets to LP where the model requires it. A mismatch — controller says NG, tank says LP — produces a crank-no-start every time on a brand-new or freshly serviced unit. If the machine has ever started properly on its current fuel, this branch is unlikely; if it never has, it’s the prime suspect, and it’s the installer’s callback.

4. Air: the filter check

Pull the air filter. A clogged filter starves the engine exactly like a fuel fault. In freezing weather, Generac calls out a sneakier version: moisture in the filter can freeze and block airflow solid. While you’re at the unit, clear the perimeter — the spec is about 3 feet of open space around it, and snow or leaf pack against the intake does the rest.

5. Cranking speed: is the battery actually delivering?

Listen to the crank itself. Strong and even = the starting system is doing its job; slow, labored, or fading across attempts = the battery can’t deliver cranking amps, and an engine cranked too slowly often won’t start even with fuel and air present. The proof is a load test, not a resting voltage reading (a dying battery reads ~12.6V at rest and collapses under load — see the battery guide). Note the battery’s age while you’re there: 3–5 years is the service life, and replacement spec for Generac air-cooled units is 12V, Group 26R, 525+ CCA.

Crank discipline: short bursts, real rests

However you work the list, crank like a technician: attempts of no more than ~8–9 seconds, a few seconds’ pause between them, 3–4 attempts per round, then a 3–4 minute rest for the starter. That cadence also purges air pockets from a freshly serviced fuel line — a legitimate cause that resolves itself if you don’t cook the starter first. Continuous cranking converts a $0 cause into a starter replacement.

Starts — then dies? Different branch

If it catches and dies within seconds, you’ve left this tree. Watch how it dies once, deliberately: fading out suggests fuel starvation; a clean, instant cut suggests a protective shutdown — low oil pressure (check the dipstick; code 1300) leads that list, with the running-stall RPM codes (1501/1511) behind it. That one observation — fade vs. cut — is the most valuable sentence you can hand a technician.

Sources: Generac official support article, “Overcrank, Code 1100-1101” (cause list, LP threshold, fuel-pressure boundary); Generac Diagnostic Repair Manual e-Code table via ManualsLib; Kohler TP-6804 fault table (“Over Crank” definition); Cummins Onan service-manual fault list (Code 4).