Generator Running but Not Producing Power: What to Check

First Question: Is the Whole House Dark?

Entire House Has No Generator Power

Check first:

• Generator output breaker
• ATS transfer state
• Controller/alarm

Some Circuits Work

Think:

• Branch breaker
• Selected-circuit design
• Load-management system
• Partial electrical fault

120V Works but 240V Loads Do Not

Possible issues include:

• Missing leg
• Breaker/connection
• ATS contact issue
• Generator output problem

That needs qualified electrical diagnosis.

Check the Generator Output Breaker

The generator's main output breaker must be ON/CLOSED for power to leave the generator.

If it is OFF:

• Determine why it is off
• Check whether recent service intentionally opened it
• Do not repeatedly reset a breaker that immediately trips

A breaker left OFF after maintenance is one of the simplest explanations for:

engine running, house dark.

Read the Controller

Confirm:

• No active alarm
• Generator is in normal running state
• Utility outage is being detected

An engine can run while the controller or transfer system prevents load transfer.

Automatic Transfer Switch

The ATS moves the house from utility to generator.

If the generator runs but the ATS does not transfer, possible causes include:

• Transfer-control wiring
• Utility sensing
• Relay/contact mechanism
• ATS control power

Read transfer switch repair →

Generator Produces No Electrical Output

If the ATS is ready to transfer but the generator itself is not producing proper output, the fault can involve:

• Breaker
• Voltage regulator
• Alternator/stator/rotor
• Excitation system
• Wiring

Portable-generator articles often discuss field flashing and residual magnetism, but that advice should not be blindly applied to automatic standby systems.

For whole-house standby equipment, internal output diagnosis belongs with a qualified technician.

Utility Sensing Problems

A standby system needs to know:

• Utility failed
• Utility returned

If sensing/control circuits are wrong, the system can behave unpredictably even when the engine runs.

Load Management

Some loads may intentionally remain off.

Typical shed loads:

• Second AC
• Water heater
• Pool equipment
• Dryer

If the house has general power but one heavy appliance stays off, check load management before assuming the ATS failed.

Generator Runs but Power Flickers

Possible causes:

• Unstable output
• Loose electrical connection
• ATS contact issue
• Overload
• Engine speed instability

Flickering under generator power is not something to ignore.

Generator Runs but Breaker Trips

If the generator output breaker trips:

• Reduce load
• Check for short/fault
• Do not repeatedly reset it

A breaker that trips again needs diagnosis.

Generator Runs but ATS Will Not Return to Utility

If utility is back but the system remains on generator:

• Confirm utility is stable
• Check controller
• Check ATS sensing/control

This is another transfer-side failure, not an engine repair.

What You Can Safely Check

Owner-level checks:

• Controller display
• Generator output breaker position
• House branch breakers
• Whether managed loads are intentionally off

Do not:

• Open energized ATS compartments
• Probe live terminals
• Bypass transfer controls

What a Technician Should Check

A proper diagnosis may include:

• Generator output voltage
• Frequency
• Both 120V legs / 240V
• MLCB condition
• Transfer-switch state
• ATS control wiring
• Utility sensing
• Load-management signals