Repair & troubleshooting
Standby generator won’t start? Diagnose the symptom before buying a part.
Start by separating four very different problems: no crank, cranks but will not start, starts then shuts down, or runs without powering the house. Then use the controller code and exact model to narrow the cause.
Do not open energized transfer-switch equipment, bypass safety controls, adjust gas regulators, test fuel pressure or work on fuel piping from an online troubleshooting guide.
Direct answer
Do not begin with “What part should I replace?”
A generator that “won’t start” can represent several different failure modes. The fastest useful information is what the engine does, what the controller displays, and the exact brand/model. Manufacturer guidance supports treating alarms as diagnostic information rather than repeatedly clearing them without correcting the cause.
Step 1 — choose the symptom
Which one describes what your generator is actually doing?
Nothing happens / engine does not crank
Look first at controller status, battery condition, battery connections and documented start-circuit faults. Briggs & Stratton's technician troubleshooting specifically identifies a weak/failed battery, charger or connections among potential no-crank causes.
Check battery specificationsEngine cranks but does not start
Do not assume the battery is the answer just because the engine turns. Capture the alarm and verify fuel availability. Fuel delivery, ignition, engine protection and brand-specific faults require a different diagnostic path.
Open repair & error-code guideIt started, then shut itself down
Treat the shutdown code as evidence. Low-oil pressure, high temperature, RPM/speed faults and other protective alarms should be investigated before repeatedly clearing and restarting the machine.
Review maintenance conditionsIt runs, but the house still has no power
That is no longer simply a no-start problem. The transfer sequence, generator disconnect and ATS may be involved. Transfer-switch equipment can contain dangerous voltage and belongs with qualified service when troubleshooting moves inside the equipment.
Find qualified local helpStep 2 — safe first checks
Collect evidence without turning troubleshooting into a repair job
Read the controller before resetting it
Photograph the exact alarm, warning, status light and error code. Codes are often controller- and model-specific, and clearing one too early can erase the best clue you have.
Decide: no crank or cranks but won't start?
No crank points the investigation toward the starting circuit, battery, connections or starter. Normal cranking without ignition sends you down a different path.
Confirm basic fuel availability
For LP, confirm there is fuel in the tank. For natural gas, note whether other gas appliances work. Do not perform regulator adjustments, fuel-pressure tests or fuel-line work yourself.
Check oil and maintenance clues
Low oil or a protective shutdown can stop operation. Use the procedure for your exact model, especially if the generator was carrying the house during an outage.
Controller alarms
The exact code matters more than a generic symptom list.
Generac, for example, distinguishes alarms such as Low Oil Pressure (1300), Overcrank, High Temperature and RPM Sense Loss families. Its current support guidance says to identify and correct the underlying issue before clearing an alarm; if it immediately returns, professional diagnosis may be required.
During an outage
A shutdown while powering the house needs a different restart procedure.
Do not treat an outage shutdown like a casual weekly exercise fault. The generator may have been carrying household load. Manufacturer procedures can require removing load before restart and restoring circuits in sequence.
Use your model’s procedure.
Generac's current outage guidance, for supported controllers, instructs owners to address the code, remove generator/household load as directed, restart in AUTO, and return loads progressively. Do not generalize those switch/button steps to another brand or controller.
Oil during extended outages
Running for days? Oil checks become part of outage operation.
Generac's current Guardian guidance says oil should be checked daily during extended outage operation and provides a load-removal/cool-down sequence before checking it. That is a Generac-specific procedure, not a universal sequence for every standby generator. Use the manual for your model.
What not to do
Avoid the expensive guesses.
Do not replace a battery solely because the generator will not start.
First establish whether the engine actually cranks and whether the controller reports a battery/start-circuit condition.
Do not repeatedly clear a returning alarm.
A returning shutdown can indicate an unresolved protective or electrical/engine condition. Preserve the code for diagnosis.
Do not open the ATS looking for a homeowner fix.
Transfer-switch equipment can involve utility and generator voltage. Stop when troubleshooting crosses into energized electrical equipment.
Professional help
Still won’t start?
Bring the model, code, symptom branch, fuel type, battery age and maintenance history with you. That turns “my generator won't start” into useful diagnostic information.