Thermador hoods that run but no longer clear the air, Mandarin

Ventilation is the appliance people call about last and should call about first, because a hood that is not moving air is quietly loading every other appliance in the kitchen with grease and moisture. It is also the appliance where the fault is most often outside the box we were called to look at.

The duct is usually the story

Mandarin’s housing stock is mostly 1970s through 1990s, built on generous lots where kitchens were extended outward rather than rebuilt. That produces long, convoluted duct runs. A hood rated for a short straight run to an exterior wall will move a fraction of its rated air through forty feet of duct with three elbows and a crushed section above a soffit, and the appliance itself will be in perfect health throughout.

The tell is a hood that has always been disappointing rather than one that got worse. Sudden loss of pull points at the appliance or at a blocked filter. Gradual, lifelong underperformance points at the duct, the termination cap, or a run that was reduced from ten inches to six somewhere it cannot be seen.

We check static pressure and look at the termination outside before condemning a blower. Where the duct is the limit we say so and put it in writing, because a new blower on a bad duct is money for nothing.

Blowers

Internal, inline and remote blowers all fail in similar ways. A motor that hums but does not start is usually a capacitor or a seized bearing, and the two are easy to separate by hand. A blower that runs only on the top speed points at the speed control rather than the motor. A blower that has become suddenly loud has almost always shed grease from one side of the wheel, unbalancing it, and cleaning it restores both the noise and the airflow.

Remote blowers mounted in an attic or on an exterior wall run hotter and collect more debris than anyone expects, and they are the ones nobody has looked at since installation. If your hood is quiet at the cooktop but you have never seen the fan, it is probably remote and probably overdue.

Downdraft systems

Downdraft ventilation has moving parts a hood does not, which gives it its own failure list. A downdraft that rises partway and stops is usually the drive belt or the lift motor, occasionally an obstruction in the track, and rarely the control. One that will not retract is the same set of parts read in reverse. Because the mechanism lives in the cabinet below the cooktop, we check for anything stored against the track before assuming a motor.

Make-up air

A professional rangetop with a high-capacity hood over it can pull more air out of a house than the house can replace. In a tightly built home the fan then works against a pressure difference it was not designed for, moves less air, and can pull outside air down a chimney or through a dryer vent.

The symptom homeowners report is a hood that seems weaker with the windows closed. If cracking a window near the kitchen visibly improves the pull, the appliance is fine and the house needs a make-up air path. We will tell you that rather than sell you a blower.

Filters and cleaning

Baffle and mesh filters are the cheapest maintenance in the kitchen and the most neglected. A saturated filter can halve airflow. Wash them properly, on a schedule that matches how you actually cook, and a good number of the calls in this section never need to be made.

The diagnostic is a flat $80, credited toward the repair when you approve the work, with ninety days on labour and three hundred and sixty-five on parts.