Onan generators: what fails first here and what it costs

Onan is the generator most owners find factory-installed in a motorhome, and portable Onan units show up on trailers and fifth wheels around Lake Conroe as well. In a hot, humid Montgomery County climate, they fail in a predictable order. Most repairs run $350 to $800, and the fix is almost always fuel, not the engine.

The failure order here

Carburetor varnish from stale fuel. Ethanol-blended gasoline left sitting through a hot, humid season absorbs moisture, separates, and leaves a gummy residue in the carburetor’s small jets. This is the top cause of a no-start call by a wide margin.
Spark plug fouling. A plug that has not fired regularly can foul, especially if the fuel problem above is also present.
Starter and solenoid. A weak or corroded connection, or a solenoid that has stuck, after months without use.
Voltage regulator or control board. Less common, but a real cause of no AC output despite the engine running, or of surging output.

What things cost

Job	Range
Trip fee	$75 to $150
Labor	$125 to $190/hr
Carburetor clean or rebuild	$350 to $800
Spark plug, fouled or worn	$150 to $300
Starter or solenoid replacement	$250 to $550
Voltage regulator or control board	$300 to $700
Routine service (oil, filters, plug, load test)	$300 to $550

Ranges from the pricing page. We diagnose in order, fuel first, since a carburetor clean does nothing for a bad starter and vice versa.

Why storage-yard idle time is the enemy

A generator’s worst enemy is sitting still. A rig parked in a gated storage yard for months, exactly the pattern for a lot of Montgomery County RVs between lake trips, is the ideal setup for fuel to go stale in the carburetor bowl and for a starter battery to slowly weaken. A monthly run under a real load (the AC, not just idling) exercises both systems and is the single cheapest thing an owner can do to prevent this call.

Before hurricane season, if you rely on it for backup power

If the plan is to use the generator during a power outage, a pre-season check and load test beats discovering a fuel problem when the power is already out. Run it outdoors only, well away from windows, doors, and any enclosed space, and confirm your carbon monoxide alarm is working before you need it.

Where we work

On site across Conroe, Montgomery, Willis, The Woodlands, Magnolia, New Caney, and Huntsville. The generator repair service page covers this in more depth.

Frequently Asked Questions

Why won't my Onan start after sitting for months?

Fuel, in the large majority of cases. Gasoline left in the carburetor bowl through a hot, humid Montgomery County season draws moisture, separates, and varnishes the jets. A carburetor clean or rebuild is the usual fix.

How much does Onan generator repair cost?

A carburetor clean or rebuild runs $350 to $800. A fouled spark plug, a bad starter solenoid, or a failed voltage regulator run in a similar range. Routine service (oil, filters, plug, load test) is $300 to $550.

How often should I run my Onan generator?

Monthly, under a real load, not just idling. A load run exercises the carburetor and the charging system in a way idling does not, and it is the cheapest thing an owner can do to avoid a no-start call after a long storage-yard sit.

Is it worth replacing an old Onan instead of repairing it?

Usually not, unless the engine itself has a major internal failure. Most Onan calls are fuel, ignition, or electrical, all of which are repairable, and replacement cost is high enough that repair is the better math in nearly every case we see.