Why Generators Fail During Storms — Ranked From the Manufacturers' Own Manuals

Troubleshooting · Updated 2026-09-01

When a hurricane or ice storm takes the grid down, generator forums fill up with the same three sentences: it won't crank, it cranks but won't start, it runs but there's no power. Most storm-prep articles answer with guesses. We have something better: the troubleshooting tables printed in the manufacturers' own service manuals.

Where these numbers come from

This site is built from a library of 3,000+ manufacturer documents. From their troubleshooting sections we extracted 10,275 complete symptom → cause → remedy entries covering 229 brands (about 4,700 distinct fixes once duplicates across model variants are merged). The ranking below counts how many distinct models' manuals document each cause — if 96 models' manuals list a cause for a symptom, that's the manufacturers themselves telling you what usually breaks. Nothing here is invented; every line traces to a real manual, and each symptom links to the full cross-brand guide with every documented cause.

Failure #1: it won't crank — and it's almost always the battery circuit

Documented for 666 distinct models. Merge the battery-family causes and they dwarf everything else: low battery (55 models), dead battery (50), bad battery connection (45), and loose, corroded or defective battery cables (39) — together the single biggest documented cluster, alongside out of fuel (96) and a blown control fuse (66).

The storm angle: a standby that exercises weekly will still crank a marginal battery — until it has to run 30 hours straight and restart hot. Batteries fail the day of the storm because they were dying for months before it. Most manuals specify replacement every 24–36 months regardless of how it tests. A between exercise cycles and a wire brush on the terminals cost less than one service call.

Full cause list: Engine will not crank · Engine does not crank

Failure #2: cranks but won't start — air, fuel and oil, in that order

Documented for 945 distinct models — the most-documented storm symptom of all. Top causes by documentation count: plugged or damaged air cleaner (63 models), defective low-oil-pressure switch (34), low engine oil (33 + 26 more as "low oil level"), incorrect fuel pressure (32), fuel shutoff valve closed (32), and defective spark plugs (30).

Read that list again: almost every entry is a maintenance item, not a breakdown. An air filter is a $15–$70 part — for example Generac's 0A4637 Amazon eBay $49.95 or Kohler's GM16944 Amazon $71.53 eBay $49.68 — and a spark plug like the RC12LC4 Amazon $31.57 eBay $26.61 is a ten-minute job. The oil-level entries matter double in a storm: low-oil shutdown protection can't tell the difference between "low oil" and "you're about to lose your freezer," so it errs on the side of the engine.

Full cause list: Engine cranks but will not start · Engine does not start

Failure #3: it runs, but nothing gets power

Documented for 350 distinct models, and here the manuals point at the electrical side: internal generator failure (50 models), a tripped main-line breaker (27), and breakers opened by overload (21). The overload entries are the storm-specific trap: a unit that carried the house fine in the spring test trips repeatedly when the well pump, sump pump and furnace all inrush together at 2 a.m. If your breaker trips on reset, shed load before assuming the unit is broken — the manuals' first-listed fix is almost universally "remove all loads, reset, reconnect one at a time."

Full cause list: No AC output voltage

Failure #4: it starts, then shuts down mid-outage

Documented for 615 distinct models. The manuals' top two causes are almost embarrassingly preventable: low oil level (60 models) and out of fuel (37 more, plus 19 as "fuel tank empty" — fill with fresh fuel, the manuals specify). Behind them: fuel-system faults on LP/NG sets (32) and low-oil-pressure shutdowns at the 14 psi threshold (18).

Mid-storm shutdowns are consumption math. A generator's fuel burn roughly doubles from half load to full load — real manufacturer curves for every size class are in our fuel-consumption tables — and "I have plenty of gas" estimates made at half load run dry overnight at full load. For gasoline sets, six-month-old untreated fuel is a documented cause, not an old wives' tale; is the cheapest insurance in this article.

Full cause list: Engine stops unexpectedly · Low oil pressure

What this ranking actually says

Sort every cause above by whether you could have fixed it the week before the storm:

• Preventable with basic service: battery + cables, air cleaner, oil level, fuel quantity and freshness, spark plugs — the overwhelming majority of documented causes.
• Fixable mid-storm with knowledge: tripped breakers, overload management, closed fuel valves.
• Genuinely needs a technician: internal generator failure, voltage regulators, control boards — a small minority of entries.

The manufacturers have effectively published the storm-prep list themselves; it's just scattered across a few thousand PDFs. We've assembled the checklist version in the companion post: the 72-hour pre-storm generator checklist.