Backup generator won't start

Q: Backup generator won't start

In Canada, when a backup generator won't start, the most common cause on a portable that has been sitting is fuel: an empty tank, a closed fuel valve, or stale gasoline gumming up the carburetor — often fixed with fresh fuel, an open valve, and the choke on. Many units also have a low-oil shutdown that blocks starting until you top up the oil. On electric-start and standby units, a dead starting battery is a frequent culprit, and a fouled spark plug can stop either type. A permanently-installed standby that won't start on its own may have a controller or transfer-switch fault, or simply be in the wrong mode — that part is licensed electrical work. One rule overrides all of this: never run a generator indoors, in a garage, or near windows and vents, and never back-feed a portable into your outlets — both can kill.

A generator that won't start is usually a small, fixable thing — stale fuel, a closed valve, low oil, or a flat battery — not a dead machine. Most of these you can rule out in a few minutes.

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Select anything that matches and the checklist below reorders to fit. Not sure? Skip it.

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In Canadian homes, start with fuel — especially on a portable that has been in storage. Check that the tank has fresh gas, the fuel valve is open, and the choke is on for a cold start. Old gasoline that has sat since last winter is the usual villain: it varnishes the carburetor and won't burn. Draining the stale fuel and refilling with fresh gas (ideally treated with stabilizer) fixes a large share of no-start portables. Never do this near any flame, and only ever run the generator outdoors, well away from windows and doors.

Ranked from real-world failure data. The order updates as you select what you’re noticing above.

Likely causes, in the order to check them

Showing the typical order

Beginner-friendly Doable, with care Safety-critical Call a pro

handymanHow to fix it

Move the generator outdoors and well clear of the building, then restore fuel: open the fuel valve, top up with fresh gasoline (treated with stabilizer), and set the choke for a cold start. If the fuel is old, drain the stale gas and the carburetor bowl before refilling.

Set the generator outdoors on level ground, well away from doors, windows, and vents, exhaust pointing away from the building — before you do anything else.
Open the fuel valve (petcock) and check the tank. If the fuel has sat since last season, drain it into an approved container and drain the carburetor bowl to clear varnished gas.
Refill with fresh gasoline, ideally treated with fuel stabilizer, set the choke closed for a cold start, and turn the engine switch to ON.
Start it (pull cord or electric start). Once it catches and warms, ease the choke open. If it still won't run on confirmed-fresh fuel, move on to oil, battery, or spark plug.

schedule30 min savings$5–30

Fresh gasoline + fuel stabilizerRegular unleaded per the manual; a stabilizer such as those sold at Canadian Tire keeps stored fuel from going stale

report Only ever run it outdoors — and never into your outletsBefore you start any generator: run it OUTDOORS ONLY, well away from doors, windows, and vents, with the exhaust pointed away from the building — never indoors or in an attached garage, even with the door open. Generator exhaust contains carbon monoxide, an invisible, odourless gas that kills people during outages every year in Canada. A battery-powered CO alarm in the house is cheap insurance. And never plug a portable into a wall outlet to power your home: back-feeding can electrocute you or a utility worker and start a fire. Powering your house from a generator safely and legally needs a proper transfer switch installed by a licensed electrician.

gavel Check your province first AB: homeowner may do this · BC: homeowner may do this · ON: homeowner may do this · PE: homeowner may do this · QC: homeowner may do this
Routine engine maintenance on a portable generator (fuel, oil, spark plug) is owner-permitted across Canada. This does NOT extend to wiring a generator into the home, which requires a licensed transfer-switch install.

verifiedWhy this one goes to a pro

A standby generator's automatic transfer switch connects your house to both the utility and the generator, and its controller manages that switchover under load. Working inside it means live, dangerous voltage and permanent fixed wiring — in Canada this is licensed electrical work in every province. Confirm the AUTO/mode setting yourself, but leave any diagnosis or repair of the controller or transfer switch to a licensed electrician.

gavel Check your province first AB: licensed professionals only · BC: licensed professionals only · ON: permit + inspection required · PE: licensed professionals only · QC: licensed professionals only
Standby generator and transfer-switch install/repair is licensed electrical work; confirm the provincial rule before presenting any of it as homeowner-permitted.

Your notes travel with the request — what you saw, what you ruled out, when it started — so the pro arrives with a head start instead of a mystery.

visibilityHow to check the spark plug

warning Make sure it can't start while you workEven a stopped engine can kick over on the recoil or fire unexpectedly. Before touching the spark plug, close the fuel valve, let the muffler cool so you don't burn yourself, and pull the plug wire/boot off. If you're not comfortable working around the engine, a spark-plug service is a cheap job for a small-engine shop.

Stop the engine, close the fuel valve, let it cool, and pull the rubber boot off the spark plug so the engine cannot possibly fire while you work.
Unscrew the spark plug with a plug socket and look at the tip: a healthy plug is dry with light tan/grey deposits; wet-black, oily, or heavily crusted means it is fouled.
Clean a lightly-fouled plug and re-gap it to the manual's spec, or fit a fresh plug of the exact part number. Reconnect the boot and try starting — outdoors only.

buildspark-plug-socketbuildratchet schedule20 min

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Why the list is in this order

We don’t sort by likelihood alone. We sort the way a good, honest tradesperson thinks: rule out the free, safe, common causes first. That’s why the cheap checks outrank the expensive repairs — and why anything dangerous gets a hard stop instead of a pep talk. The order exists to save you money, not to sell you anything.