Most ducted range hoods, including La Cornue’s, use a backdraft damper — a set of flaps in the duct that open when the fan pushes air through them and close on their own once the fan stops, to keep outside air, insects, and cold drafts from coming back down the duct into the kitchen. It is a simple mechanical part, and when it sticks, the way it fails tells you a lot about what to check next.
Stuck Closed: Looks Like a Dead Motor
A damper stuck closed blocks the fan’s output even if the motor is spinning perfectly normally, which shows up to the user as weak or absent suction — a complaint that sounds exactly like a failing motor from the kitchen side, even though the motor is doing its job against a duct that will not open. Grease residue gluing the flaps shut, or a flap that has warped slightly out of alignment, are the usual reasons a damper sticks in the closed position.
Stuck Open: A Different Set of Signs
A damper stuck open, by contrast, does not block airflow — it lets outside air move freely down the duct whenever the fan is off, which shows up as a cold draft near the hood, an odor from outside coming back into the kitchen, or a faint whistling sound on windy days. This is a comfort and nuisance issue rather than a suction problem, and it is easy to overlook for a long time since the hood still works normally whenever it is actually running.
Why This Matters Before Blaming the Motor
Because a stuck-closed damper mimics motor failure so closely, checking the damper is a quick, low-cost step worth doing before assuming a hood with weak suction needs a new motor. It is also worth checking the duct run itself for a crushed or disconnected section, since that produces a similar suction complaint through an entirely different cause.
What Maintenance Prevents Here
Grease that reaches the duct beyond the filters is what glues a damper shut over time, so the same filter maintenance that protects the blower wheel also protects the damper — one more reason grease management at the filter stage matters more than it might seem for a part you rarely see or think about.
Why This Is Not a Casual Fix
The damper sits inside the duct connection at the hood, often behind the same housing that holds the blower and its electrical connections, so freeing or replacing a stuck damper is not simply a matter of reaching in with a cloth. With the power isolated, a technician can access and service the damper without disturbing the wiring around it.
If your hood’s suction has dropped, or you have noticed a draft coming back down the duct when the fan is off, a La Cornue range hood repair visit checks the damper before assuming the motor is the cause.