Generator Repair: Common Problems, Costs & When to Call a Technician

Why Won't My Generator Start?

There are several common reasons.

The most useful first split is:

Generator Does Not Crank

The engine does not turn over.

Potential causes include:

• weak/dead battery
• battery connection problem
• blown fuse
• controller not in AUTO
• starter/starting circuit issue

Generator Cranks but Does Not Start

The engine turns but does not fire.

Potential causes include:

• fuel problem
• regulator/pressure problem
• ignition issue
• overcrank condition
• blocked air supply
• controller fault

Generator Starts Then Stops

Potential causes include:

• low oil pressure
• RPM-sense fault
• overload
• fuel starvation
• electrical/control fault

That distinction immediately narrows the diagnosis.

Start With the Fault Code

Modern standby generators often tell you why they stopped.

Before resetting anything:

write down or photograph the alarm/error code.

That can save a technician a lot of time.

A common mistake is:

1. generator faults
2. homeowner clears the alarm
3. generator faults again
4. nobody remembers the original code

The code is diagnostic evidence.

Keep it.

Generator Won't Crank

If the generator does absolutely nothing when told to start, begin with the starting system.

Check Whether It Is in AUTO

This sounds stupid until it isn't.

A standby generator left in:

• OFF
• manual/service state

may not start automatically when utility fails.

Kohler's current troubleshooting guidance specifically includes checking whether the generator is OFF and restoring the appropriate RUN/AUTO state as one of its first basic checks.

Check the Starting Battery

A weak battery is one of the first things manufacturers tell owners to inspect.

Kohler's current residential troubleshooting guidance lists a weak/dead starting battery and poor battery connections among the basic causes of a generator that will not crank.

A battery can have some voltage and still fail under starter load.

That's why a proper:

battery load test

is more useful than simply seeing 12 volts on a multimeter.

See our generator battery replacement guide.

Generator Battery Is Dead

A dead battery may mean:

• battery reached end of useful life
• terminals are loose/corroded
• charger is not maintaining it
• generator has a charging fault
• battery has been repeatedly discharged

Do not immediately conclude:

“Bad battery.”

If the replacement battery also goes flat, the charging system needs diagnosis.

Our existing Generac research also distinguishes between controller messages indicating a battery should be inspected and evidence that it has definitively failed.

Generator Cranks but Won't Start

If the starter is turning the engine, the problem shifts towards:

• fuel
• ignition
• air
• controls

For gaseous standby generators, fuel supply becomes one of the big suspects.

Generac's current troubleshooting guidance for represented standby systems directs owners to contact an authorised service dealer where an RPM-sense/start fault returns and identifies possible fuel issues as one area requiring investigation.

Check the Fuel Supply

For natural-gas and propane generators, basic checks can include:

• is the fuel shutoff open?
• is the propane tank actually filled?
• has gas service been interrupted?
• did someone close a valve?
• are other gas appliances working?

Do not adjust:

• regulator pressure
• gas valves
• internal fuel components

without appropriate competence/equipment.

A standby generator can have enough fuel to exercise at light load but still be starved when the house demands substantial power.

That is a fuel-system design problem, not simply a “generator won't start” problem.

Generator Says Overcrank

An overcrank fault generally means the generator attempted to start but failed within its programmed starting sequence.

Potential causes can include:

• lack of fuel
• fuel pressure problem
• ignition problem
• starting-system issue

Generac's represented current guidance says an overcrank condition should be cleared and a manual start attempted; if the generator still does not start or runs roughly, the owner should contact an authorised service dealer.

That is a sensible boundary.

Do not keep forcing repeated start cycles indefinitely.

Low Oil Pressure Alarm

A low-oil-pressure shutdown deserves attention.

The first check is:

oil level.

Generac's current owner guidance says to check the oil level and add oil according to the owner's manual; if oil level is correct and the low-pressure fault remains, contact an authorised service dealer.

That distinction matters.

Low oil level can be straightforward.

Correct oil level + low oil pressure may indicate:

• sensor
• wiring
• actual lubrication problem

Continuing to run the engine is not the smart experiment.

Generator Starts and Then Shuts Off

If a generator starts normally but shuts down soon afterwards, look for:

• alarm code
• overload
• fuel starvation
• low oil pressure
• RPM-sense fault
• overheating/airflow issue
• controller issue

Do not automatically assume the engine itself has failed.

The shutdown may be the generator protecting itself.

Generator Runs but the House Has No Power

This is a different fault.

The engine is running.

The power is not reaching the house.

Possible areas include:

• generator output breaker
• automatic transfer switch
• service disconnect
• control/sensing wiring
• utility/ATS state
• generator alternator/output problem

This is where homeowners often start poking around electrical equipment they should not be opening.

Don't.

Check the Generator Breaker

A tripped generator breaker can stop output reaching the transfer system.

If the breaker tripped because the generator was overloaded, remove/reduce excessive loads before resetting according to the manufacturer's instructions.

If it trips again:

stop resetting it.

Kohler's current residential guidance specifically says that if the generator-set circuit breaker trips repeatedly, an authorised distributor/dealer should be contacted for service.

Repeated protective-device operation is evidence of a problem.

Treat it that way.

Transfer Switch Problems

A perfectly healthy generator is useless if the transfer switch does not connect it to the house.

Potential ATS problems include:

• failed contactor
• controller fault
• utility sensing issue
• generator sensing issue
• wiring/communication problem
• mechanical failure

Symptoms might include:

• generator starts during outage but house stays dark
• generator never receives start signal
• house fails to return to utility power
• switch repeatedly attempts to transfer

Transfer equipment can contain utility/service voltage even when the generator itself is off.

This is technician/electrician territory.

See our generator transfer switch guide.

Generator Starts When There Is No Power Outage

Not every unexpected start is a fault.

Possible explanations include:

• scheduled exercise
• utility brownout/voltage event
• controller sensing issue

Generac's current support guidance specifically advises owners to distinguish normal exercise and utility-voltage issues from an actual fault when a standby generator starts while utility appears to be available.

If it is starting repeatedly outside scheduled exercise, investigate.

Generator Won't Exercise

A standby generator that fails its scheduled exercise may have:

• battery problem
• fault/alarm
• incorrect controller state
• scheduling/configuration issue
• fuel issue
• starting-system fault

Do not ignore failed exercise cycles.

The whole purpose of automatic exercise is to reveal some problems before the real outage.

Generator Runs Rough

Rough operation can come from:

• fuel delivery
• ignition
• air restriction
• plugs
• regulator problems
• contaminated fuel on liquid-fuel systems
• engine condition

Kohler's current troubleshooting material lists issues such as clogged air cleaners and weak battery conditions among possible causes when represented generators start hard, lack power or operate erratically.

If a gaseous standby generator suddenly starts running poorly under real household load, fuel supply deserves particular attention.

Natural Gas Generator Repair

Natural-gas generator faults can involve:

• meter capacity
• regulator
• gas pressure
• fuel solenoid
• fuel mixer
• piping
• ignition

A particularly important distinction is:

generator repair vs installation defect.

If a generator repeatedly starves for fuel under high load because the gas line is undersized, replacing generator parts does not fix the actual problem.

See our natural gas generator guide.

Propane Generator Repair

Propane-related faults can involve:

• empty/low tank
• regulator
• fuel pressure
• vaporisation
• low-temperature conditions
• valves
• hoses/piping

A propane generator may have fuel in the tank but still experience inadequate fuel delivery if the tank/fuel system cannot vaporise and deliver propane at the required rate.

That's especially relevant during:

• cold weather
• high generator load

See our propane generator guide.

Diesel Generator Repair

Diesel introduces a different set of problems:

• contaminated fuel
• water
• fuel filters
• injectors/fuel delivery
• cold-weather starting
• starter battery
• coolant
• engine-system faults

Stored diesel fuel quality can become part of the repair diagnosis.

See our diesel generator guide.

Portable Generator Repair

Portable generators share many engine problems with standby equipment but add storage-related issues.

Common examples include:

• stale gasoline
• carburettor contamination
• fuel blockage
• recoil/electric start problems
• dirty air filter
• spark plug
• low-oil shutdown
• overloaded outlets
• damaged receptacles

A gasoline portable generator that has sat unused for two years with old fuel in it is a very different repair problem from a natural-gas standby generator.

See our portable generator guide.

Portable Generator Starts but Produces No Power

Possible causes include:

• tripped breaker
• overload
• outlet/GFCI issue
• alternator/excitation problem
• internal electrical fault

Reset user-serviceable protection only according to the manual.

If output still does not return:

get it diagnosed.

Generator Keeps Tripping the Breaker

First ask:

is it overloaded?

If connected loads exceed generator capacity, reduce demand.

For a panel-connected system, switch off large loads such as:

• water heater
• dryer
• range
• second AC
• pool equipment

Then restore loads gradually.

If the breaker trips at a load it previously handled — or trips repeatedly with low load — stop treating it as normal overload.

Get it serviced.

Generator Overload vs Generator Fault

These get confused constantly.

Overload

Generator demand is too high.

Solution:

• reduce electrical load
• improve load management
• possibly resize the generator

Generator Fault

The generator cannot properly supply a load it should be capable of carrying.

Potential cause:

• engine
• fuel
• alternator
• controller
• breaker
• wiring

Don't keep buying a bigger generator to compensate for a faulty existing one.

Generator Won't Run Central AC Anymore

If a generator previously ran the AC successfully but now struggles, possibilities include:

• AC starting requirement changed
• failing AC capacitor/compressor
• generator fuel issue
• reduced generator output
• overload from other loads
• voltage/frequency issue

The generator may not be the only equipment at fault.

That is why good diagnosis matters.

Generator Voltage Is Low

Low generator voltage can be caused by problems including:

• overload
• engine speed
• alternator/regulation
• fuel starvation
• electrical fault

Do not start adjusting voltage regulators from an internet tutorial unless you actually know the equipment.

A bad adjustment can convert one repair into several.

Generator Frequency Is Wrong

Generator frequency is tied to engine/control operation.

Abnormal frequency can point towards:

• engine speed problem
• load problem
• controller/governor issue
• fuel delivery

Again:

diagnose the cause.

Do not simply adjust until the display looks nicer.

Generator Battery Keeps Dying

If a replacement battery repeatedly goes flat, investigate:

• charger
• connections
• parasitic draw
• controller power
• charging supply
• battery condition

Replacing batteries indefinitely is not diagnosis.

See our generator battery replacement guide.

Generator Control Board Replacement

Controller faults can become expensive because modern standby generators rely heavily on electronics for:

• starting
• sensing
• exercise
• transfer coordination
• fault monitoring

Before replacing a controller, competent diagnosis should rule out:

• power supply
• battery
• wiring
• sensors
• communication

A fault code mentioning a controller does not always prove the board itself is dead.

Generator Starter Replacement

Symptoms can include:

• clicking
• no crank
• intermittent crank

But battery problems can mimic starter failure.

Always establish:

• battery condition
• terminal condition
• voltage under load

before paying for a starter.

Generator Alternator Repair

Alternator/generator-end problems are less DIY-friendly.

Symptoms can include:

• engine runs but no output
• low voltage
• unstable output
• breaker issues

This requires electrical diagnosis.

On an older portable generator, alternator repair may exceed sensible replacement economics.

On an expensive permanent standby system, repair is much more likely to make financial sense.

Automatic Transfer Switch Repair

ATS repair can involve:

• contacts
• sensing
• controls
• wiring
• mechanical transfer components

Because transfer switches sit directly in the electrical-power path, use someone competent with generator transfer equipment.

A general engine mechanic is not automatically the right technician.

Generator Repair vs Maintenance

These are different.

Maintenance

Work performed to prevent problems:

• oil
• filters
• spark plugs
• battery testing
• inspection

Repair

Work required because the system is malfunctioning.

If maintenance has been neglected long enough, the two overlap.

See our whole-house generator maintenance guide.

Generator Repair vs Replacement

This is the commercial decision on an older generator.

I would compare:

repair cost + expected remaining service value

against:

replacement cost + benefits of current equipment.

Replacement becomes more attractive when:

• major parts are obsolete
• several systems are failing
• generator is badly undersized
• enclosure/engine/controller are all deteriorating
• service support is disappearing
• expensive repair buys very little future utility

When Is Generator Repair Worth It?

Usually when:

• fault is isolated
• replacement parts are available
• engine/generator are otherwise sound
• machine still fits the home's load
• repair is a modest percentage of replacement cost

Standby generators are expensive installed systems.

Replacing an otherwise healthy unit because of a repairable component can be terrible economics.

When Should You Replace Instead?

Replacement deserves serious consideration when the existing generator:

• requires major engine work
• needs multiple expensive systems repaired
• cannot handle current household load
• lacks parts/service support
• has extensive corrosion/damage
• would require expensive upgrade work anyway

Don't apply car-style:

“repair costs more than the generator's resale value”

logic blindly.

The relevant comparison is the cost of restoring backup capability.

Warranty Repair

Before paying out of pocket, check:

• generator serial/model
• installation date
• warranty
• dealer status
• maintenance records

Manufacturers may require authorised service and evidence of scheduled maintenance for covered repairs.

Do not authorise a $2,000 repair before checking whether the component is under warranty.

Generac Generator Repair

Generac provides extensive fault-code guidance for basic owner checks but repeatedly directs owners to an Independent Authorized Service Dealer where faults persist or require technical diagnosis.

For serious repair, I would prefer a technician who works regularly on:

• Generac controllers
• Evolution / Power Zone systems
• Generac ATS equipment
• gaseous fuel systems

See our Generac maintenance guide.

Kohler / Rehlko Generator Repair

Kohler/Rehlko's current troubleshooting guidance advises owners to check simple items such as:

• starting battery
• loose connections
• breaker state

and to contact an authorised dealer where the manual does not resolve the problem or protective devices repeatedly trip.

Rehlko also currently routes generator service and repair through its certified dealer network.

Cummins Generator Repair

Cummins is even more explicit.

Its current home-generator FAQ says that if a professionally installed home standby generator is not running, owners should contact a Cummins-authorised service provider.

That's sensible for modern QuietConnect equipment.

The controller, fuel and electrical systems should be diagnosed as a system.

Briggs & Stratton Generator Repair

For Briggs standby systems, use technicians familiar with:

• PowerProtect / PowerProtect+
• Symphony Choice
• EnergyTrak
• Vanguard engines
• Briggs ATS equipment

Especially if warranty coverage applies.

The brand-specific controls matter as much as the engine.

Champion Generator Repair

Champion likewise spans very different equipment:

• standby fleX/aXis
• conventional portable
• inverter
• dual-fuel
• tri-fuel

A technician who understands a gasoline portable carburettor is not automatically competent to diagnose a 26 kW automatic standby system.

Match the technician to the equipment.

Can an Electrician Repair a Generator?

Sometimes.

Electrical faults may require an electrician.

Engine/fuel faults may require a generator technician.

Standby systems often combine:

• engine
• gaseous fuel
• automatic controls
• service-voltage electrical equipment

The best generator-service companies employ or coordinate the relevant disciplines.

Don't assume any electrician is automatically a generator specialist.

Can an HVAC Technician Repair a Generator?

Not generally unless they also have generator-specific capability.

They may understand:

• natural gas
• electrical controls

but that is not enough to make them competent with every generator system.

Use specialists for specialist equipment.

Can You Repair a Generator Yourself?

Some owner-level work is reasonable.

Potentially:

• check oil level
• check breaker state
• inspect obvious battery terminals
• replace routine filters/plugs where manual allows
• follow manufacturer troubleshooting steps

I would not casually DIY:

• gas-pressure adjustments
• ATS work
• controller replacement
• internal high-voltage work
• engine internals
• safety-system bypasses

The question isn't:

“Could I technically do it?”

It's:

“Does DIY create enough economic upside to justify the risk of misdiagnosing a machine connected to gas and household electrical service?”

Usually not on a $10k+ standby system.

What to Tell the Generator Technician

Before calling, gather:

1. brand
2. exact model
3. serial number
4. fuel
5. generator age
6. fault code
7. whether it cranks
8. whether it starts
9. how long it runs
10. whether house receives power
11. recent maintenance history
12. anything that changed before the fault

That makes the service call more efficient.

What Should a Generator Repair Technician Test?

Depending on the fault, proper diagnosis can include:

• battery/load test
• charging system
• stored fault history
• starter system
• ignition
• oil level/pressure
• fuel pressure
• regulator/fuel delivery
• engine operation
• output voltage/frequency
• breaker
• ATS function
• load test

The goal should be:

prove the failure.

Not:

replace parts until it starts.

Ask for a Load Test

A generator can:

• start
• run
• exercise

and still fail under real household load.

After relevant repairs, ask whether the system was tested:

under load.

Especially when the original complaint was:

• shutdown during outage
• poor AC starting
• breaker trip
• fuel starvation
• unstable output

A successful no-load start is not always proof of repair.

Emergency Generator Repair During an Outage

Storm-period service is a different market.

You may face:

• high call volume
• parts shortages
• prioritisation of contract customers
• travel delays

This creates a commercial reason to have:

• known service provider
• maintenance relationship
• model/serial recorded
• essential spares where appropriate

before the outage.

Waiting until the generator fails during a regional emergency is the worst time to start searching for somebody who services your brand.

Generator Service Contracts

Service plans can make sense when they include useful things such as:

• scheduled maintenance
• priority emergency response
• remote monitoring
• discounted labour
• annual transfer/load testing

But read the scope.

A “maintenance plan” is not necessarily:

unlimited repairs.

Compare:

• included visits
• consumables
• travel
• emergency priority
• repair labour

before buying.

How to Choose a Generator Repair Company

I would prioritise:

1. experience with the exact brand
2. authorised status where warranty matters
3. standby-system experience
4. gas/electrical competence
5. diagnostic capability
6. emergency response
7. parts access
8. transparent callout/labour pricing

Review count and star rating are secondary signals.

The technician needs to understand the machine.

Does the Repair Company Need to Be an Authorised Dealer?

Not for every out-of-warranty job.

But authorised service can matter when:

• warranty is active
• proprietary diagnostic systems are involved
• parts/software access matters
• manufacturer reimbursement is required

Generac, Kohler/Rehlko and Cummins all currently maintain authorised/certified service channels for their home standby equipment.

Generator Repair Checklist Before Calling

Before booking service, safely check:

• controller is in correct operating mode
• fault code is recorded
• oil level
• visible battery connections
• fuel supply
• generator breaker
• obvious obstruction/debris
• whether utility power is actually present

Do not open service-voltage equipment or alter gas components.