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The work is split between trades. A technician trained on the equipment services the engine, controller and alternator; a licensed electrical contractor handles the transfer switch, interlock, inlet and wiring to the panel; and a licensed gas technician works on any natural gas or propane supply. This page covers the warning signs, common failures, what a service call involves, repair-versus-replace decisions and the safety rules that matter most when a generator isn't working properly.
Signs your generator needs repair: missed exercise runs, fault lights and power that won't transfer
- The standby unit skipped its scheduled exercise run, or the controller shows a fault, service or low-battery warning.
- The power went out and the generator started, but the house stayed dark, which points to the transfer switch or its controls.
- The engine cranks slowly, clicks or won't turn over, often a weak starting battery on a cold morning.
- Lights flicker or dim when the generator carries the house, or it shuts down as soon as the furnace blower or sump pump kicks in.
- Oil, fuel or coolant is leaking under the unit, or you hear knocking or see heavy smoke from the exhaust.
- A portable unit only runs with the choke on, dies after a few minutes or surges up and down.
Common standby and portable generator problems and their causes
- Starting batteries weaken with age and cold, and a dead battery is a frequent reason a standby unit fails to answer an outage.
- Gasoline that sits in a portable generator's tank and carburetor goes stale and leaves gummy deposits that block the fuel passages.
- A failed relay, control board or worn contacts in the transfer switch can leave a healthy generator running with nothing connected to it.
- Safety shutdowns for low oil pressure, overheating, overspeed or repeated failed starts protect the engine but leave you without power until the cause is fixed.
- Mice and other animals nest inside enclosures and chew wiring, and drifting snow or ice can block the air intake and exhaust.
- Circuits added to the house after installation can overload a unit sized only for essential loads.
What a generator service and repair visit includes
- The technician reads the controller's fault history and asks what happened during the last outage.
- Engine checks cover oil level and condition, air and fuel filters, spark plugs, belts, coolant on liquid-cooled units and the battery under load.
- For portables, the tank and carburetor are drained, cleaned or rebuilt; for standby units, any leak or pressure problem on the gas supply goes to a licensed gas technician.
- A load test, with the generator carrying real household circuits, shows whether it holds steady voltage and frequency.
- A licensed electrician tests and repairs the transfer switch or interlock, the inlet and the connections at the panel.
- The exercise schedule and any remote monitoring are reset, and you get a written report of what was found and replaced.
Using a generator safely while it's being repaired: backfeeding and carbon monoxide
Many generator accidents happen when the proper connection is out of service and someone improvises. The two most dangerous shortcuts are feeding the house through an outlet and running the engine somewhere sheltered from the weather.
- Never push power into the house through a receptacle, a dryer or range outlet included; BC Hydro warns that plugging a portable generator into a regular household outlet can back-feed the grid, a serious electrical danger to neighbours and utility workers.
- Until the transfer switch or interlock is fixed, plug appliances directly into the generator using a heavy-duty outdoor extension cord, as Toronto Hydro advises.
- Run the generator outdoors only, well away from open windows and doors; Toronto Hydro warns that generators used in garages, sheds or on covered porches produce carbon monoxide that can be fatal.
- If you feel dizzy, nauseous, drowsy or short of breath while a generator is running, get to fresh air immediately and seek medical attention.
- Keep a working carbon monoxide alarm near the bedrooms, as Health Canada recommends, and test it before storm season.
Generator fuel storage and care after a long outage
Fuel is behind many portable generator repairs and some serious accidents. Health Canada advises keeping gasoline and other fuels out of the house, tightly closed, ideally in a separate building that isn't connected to the home's ventilation, and BC Hydro calls for labelled, vented fuel containers stored in a well-ventilated shed away from living areas. ESA notes that gasoline and its vapours are extremely flammable, and advises letting the engine cool for at least 2 minutes before refuelling and always using fresh gasoline.
- After a long outage, have a standby unit serviced even if it ran perfectly, since days of continuous running use up oil and filters much faster than exercise runs.
- Follow the manual's service intervals, which are often counted in running hours as well as months.
- Have the starting battery tested each fall, before cold weather exposes a weak one.
- Keep snow, leaves and plants clear of a standby unit's enclosure, air intake and exhaust all year.
Repair or replace a home generator?
Most failures are routine repairs: batteries, filters, spark plugs, sensors, carburetors and transfer switch components. Replacement becomes the better choice when the engine or alternator has failed on an older unit, when parts or dealer support are no longer available, when the household now needs more backup than the generator was sized for, or when a portable unit that sat unused for years would need a full overhaul.
A new standby generator is an installation job rather than a repair, with its own electrical notification or permit and gas connection; our generator installation page covers sizing, transfer equipment and placement.
Who repairs what: generator technicians, licensed electricians and gas technicians
A technician trained on your equipment can repair the engine and controller, and many standby generator warranties expect service by an authorized dealer, so check before hiring. Anything that touches your home's wiring, including the transfer switch, interlock, inlet and panel connections, is electrical work. ESA states that a standby generator permanently connected to a home's wiring must have a transfer device, and that by law anyone you hire for electrical work must be a Licensed Electrical Contractor. In Quebec, that work goes to a contractor licensed through the CMEQ. Repairs to a natural gas or propane supply belong to a licensed gas technician, such as a TSSA-registered fuels contractor in Ontario.
Generator Repair: frequently asked questions
Why won't my standby generator start when the power goes out?
The usual suspects are a weak battery, a fuel supply problem, a controller left in off or manual mode, or a safety lockout after an earlier fault. Check the controller's display, but don't keep resetting it; a repeated fault needs a technician to find the cause.
My generator is running but the house has no power. What's wrong?
The problem is most likely in the transfer switch, its controls or the wiring to the panel. That's electrical work for a licensed electrician; in the meantime, don't try to bypass the switch, and run essential appliances on cords plugged directly into the generator.
Can I power the house through the dryer outlet until the transfer switch is fixed?
No. Feeding power through any household outlet can back-feed the grid and energize lines that crews believe are dead, and the exposed plug of the cord can be live. Plug appliances into the generator directly until a licensed electrician repairs the transfer equipment.
Why does my portable generator run rough or stall after a few minutes?
Old fuel is the most common cause: gasoline that sat in the tank and carburetor for months can clog the fuel system. ESA advises always using fresh gasoline. A dirty air filter, fouled spark plug or low oil level can cause the same symptoms, so have the unit serviced if fresh fuel doesn't fix it.
How often should a home generator be serviced?
Follow the manufacturer's schedule, which usually combines running hours and elapsed time. As a practical habit, book a check before winter storm season and again after any long outage, when the unit may have run for days.
Sources
- BC Hydro: Power during outages, generators and device chargers
- Toronto Hydro: What to do during an outage
- Electrical Safety Authority: Generator safety
- Electrical Safety Authority: What you need to know about electrical work
- Health Canada: Use household chemicals safely
- Health Canada: Preventing carbon monoxide exposure
- CMEQ: A licence is mandatory
- TSSA: Authorized heating fuel contractors (Ontario)
Written by the LokalMatch editorial team. Reviewed by Zubair Afzal on September 10, 2026. How we write and check our guides