Why standby generators fail
When a standby generator does not start during an outage, the cause is rarely dramatic. It is almost always something that had been quietly deteriorating for months while the unit sat waiting.
The weekly self-test helps, but it runs the engine briefly with no electrical load. It confirms the unit can start. It does not confirm it can carry your house.
- A dead or weak starting battery, by far the most common cause
- Stale fuel or a fuel supply problem, particularly with propane
- Oil degraded by long idle periods and short test runs
- Rodents nesting in the enclosure or chewing wiring
- A corroded or seized transfer switch
- Air intake or cooling passages blocked by debris
- Control board faults that never surface until load is applied
Batteries are the usual culprit
Most no-start failures come down to the battery. It sits in an unheated enclosure through a New England winter, and it is not obviously flat until the day it is needed. Batteries are consumable and should be replaced on schedule, not on failure.
What an annual service covers
Servicing a standby generator has two halves: the engine, which is largely conventional, and the electrical and control systems, which are where an electrician adds most.
- Oil and filter change, with the correct grade for the season
- Air filter inspection or replacement
- Spark plug inspection and replacement at interval
- Battery load test and terminal cleaning
- Fuel system and supply pressure check
- Coolant check on liquid-cooled units
- Enclosure inspection for rodents, corrosion, and blockages
- Transfer switch inspection, including contacts and terminations
- Control board and self-test schedule verification
- Test under actual electrical load, not just an idle run
Testing under load, not just starting it
This is the part most often skipped, and it is the part that finds real problems. Starting a generator proves the starter and the battery work. It says nothing about whether the unit can hold voltage and frequency while your house is drawing power.
We simulate an outage so the transfer switch operates and the generator carries the actual load, then verify the transfer back when utility power returns.
- Voltage and frequency held under load
- Transfer switch operating correctly in both directions
- Load management shedding and restoring as configured
- Engine reaching and holding operating temperature
- No alarms or faults logged during the run
How often, and when
Annual servicing suits most residential standby units. Units that run frequently, or that carry critical load in a commercial setting, are usually serviced by run hours instead.
Timing matters as much as frequency. Servicing in late summer or early autumn means any parts needed arrive before storm season, rather than during it when everyone else has discovered the same problem.
- Residential standby: annually, or per the manufacturer's hours
- Commercial and critical: semi-annual is common
- After any extended run, such as a multi-day outage
- Batteries replaced on schedule rather than on failure
- Best booked before storm season, not after an outage
How a service visit runs
- 1
Review history and alarms
We check the run log, hours, and any stored faults before touching anything. The log often explains a symptom the owner has not noticed.
- 2
Engine service
Oil, filters, plugs at interval, and a full inspection of the enclosure, intake, and cooling.
- 3
Electrical and control checks
Battery load test, transfer switch inspection, terminations checked, and the self-test schedule verified.
- 4
Simulated outage under load
We drop utility power, confirm transfer, run under real load, and confirm transfer back. Then you get a written report of condition and anything needing attention.
Repairs and units we service
We service and repair standby generators regardless of who installed them. If you inherited a unit with a house and have no idea when it was last touched, that is a common starting point and a good reason to book a baseline service.
- No-start and intermittent starting faults
- Transfer switch failures and contact damage
- Battery, charger, and control board replacement
- Fuel supply and regulator problems
- Alarm and fault code diagnosis
- Condition assessment on inherited or neglected units
Related generators services
Jobs we're often asked about alongside this one.
Frequently asked questions
- How often should a standby generator be serviced? +
- Annually for most residential units, or by run hours per the manufacturer. Commercial and critical installations are often semi-annual. Also service after any extended run, such as a multi-day outage.
- The weekly self-test runs fine. Is that enough? +
- No. The self-test runs the engine briefly with no electrical load. It confirms the unit starts. It does not confirm it can hold voltage and frequency while carrying your house, which is where real faults appear.
- Why do generators fail to start when needed? +
- Most often the battery, which sits in an unheated enclosure through winter and is not obviously flat until the moment it is needed. After that, stale fuel, degraded oil, rodent damage, and seized transfer switches.
- When is the best time to book a service? +
- Late summer or early autumn, before storm season. Any parts needed arrive while supply is normal, rather than during the week when everyone else has just discovered the same problem.
- Do you service generators you did not install? +
- Yes. Inheriting a unit with a house is common, and a baseline service tells you its condition, whether it has been maintained, and what it will need.
- How long does a service take? +
- Typically two to three hours for a residential unit, including the load test and transfer verification. Longer if the log shows faults that need investigating.