Generator won’t start

Note the exact Start behavior first. A generator that cranks but won’t fire is a different problem than one that clicks dead. Hour meters, fault blink codes, and fuel that sat through storage matter more than guessing a control board. Write down what happens when you press Start: click, slow crank, fast crank/no fire, start-then-die, or start-with-no-load. That single observation cuts the diagnostic tree in half. Keep the bay ventilated; do not keep cranking into a fuel smell.

Symptoms

• Click, no crank — or slow, labored cranking
• Cranks strong, never fires
• Starts, runs a few seconds, then dies (with or without a blink code)
• Starts and runs, but no 120V to the coach (breaker / transfer path)
• Low-oil or other safety shutdown shortly after start
• Won’t start after long storage; stale fuel or closed generator fuel tap suspected
• Hour meter high; overdue oil / filter service coinciding with the no-start

Quick path (owner-safe)

1. Coach batteries strong enough to crank? Try with charger/shore support. Voltage under crank tells more than resting voltage alone.
2. Oil level / low-oil shutdown; prime per OEM if equipped. Low oil is a common “mysterious” no-start after a move or a slope park.
3. Note any fault blink codes (Onan and others). Count the blinks twice; photo the service-manual page if you have it.
4. Fuel age and valve position after storage. Stale gasoline and a closed generator fuel tap are classic post-winter fails. LP units: confirm tank valve and regulator supply with another appliance only if safe to do so.
5. Air filter obvious blockage; remove nesting if present — don’t vacuum into the carb throat.
6. Confirm the generator breaker and transfer-switch path only after it runs no-load — no-load vs no-start are different tickets. Never force a transfer under load you haven’t metered.

Symptom forks

• Click, no crank — battery, cables, starter solenoid, ground. Borrow voltage from shore/charger before condemning the starter.
• Cranks, no start — fuel, spark/glow (diesel), safeties, control board, air filter / carb varnish on gas units.
• Starts, then dies — fuel delivery, vapor lock / heat soak, safety sensor, or auto-stop on fault code.
• Starts, no load / no coach power — generator breaker, EMS, transfer switch, or load issues — see the full generator guide before replacing the genset. Related electrical: no power / dead coach · inverter / shore-power faults.
• High hours, marginal oil history — service first; a no-start after neglect is often oil/fuel/spark, not a new unit.

Owner checklist

• Generator brand/model and hour meter reading (Onan / Cummins Onan, and other labels as fitted — read the data plate).
• Fuel type (gas / diesel / LP) and how long the coach sat; last fuel additive or stabilizer use.
• Exact Start behavior and any blink code count (photo).
• Whether shore power / inverter is available as a backup while we diagnose.
• Recent oil / filter service dates if known.
• Coach location for a trip quote (Prefer Text).

Fuel, oil, battery, hours, transfer-switch safety

Fuel that sat months gums carburetors and starves injectors; diesel gels and grows algae in the wrong climate. Oil below the mark trips safeties that look like “bad boards.” House batteries that show 12.4V resting can still collapse under crank — measure during the attempt. Hour meters guide service intervals; skipping oil changes is how no-starts become short blocks.

Transfer switches and automatic transfer devices are not DIY poke-points while shore and generator can both be live. If the genset runs fine on its own breaker but the coach never sees power, stop at the transfer path and Prefer Text — mis-wiring or a welded contactor is a shock and equipment hazard, not a YouTube swap.

When to stop DIY

• Fuel smell in the bay, wet carb, or diesel leaks — do not keep cranking.
• Opening sealed control boards or “flashing” controllers from random forums.
• Running with known low oil after a shutdown — that is how you buy a short block.
• Transfer switch work you are not metered for while the coach is on shore or the genset is running.
• LP smell or suspected gas leak in a generator / LP bay — shut off, ventilate, Prefer Text or emergency services as appropriate.

What UMRT diagnoses

Mobile generator diagnosis: cranking voltage, safeties, fuel path, hour-based service gaps, and fault-code interpretation (Onan / Dometic index where applicable). We are Dometic Professional Certified for appliance-adjacent work; generator service here is diagnostics-first, not parts roulette, and we do not invent OEM “factory certified” titles beyond credentials we actually hold. Labor ~$150/hr (1 hr min / 30-min); diagnostic $175 applied if you proceed. Trip $75 / 30 mi then $1.50/mi. Prefer Text — corridor MT · WY · ID · WA.

Related guides & siblings

Deep dive: Generator troubleshooting · Onan / Dometic fault index · Generator service. Related: No power · Inverter / shore-power faults · 12V battery no-charge. Hub: Troubleshoot.

Prefer Text — (616) 606-5277. Trip $75/30 mi then $1.50/mi · labor ~$150/hr (1 hr min / 30-min) · diagnostic $175 applied · winterize $175 · trip-prep $225. Credentials: Victron Professional Certified Installer · weBoost Authorized Installer · Peplink Certified Associate · Dometic Professional Certified.