Thermador Hood Repair: Weak Extraction, Dampers

Ventilation is the category where the appliance is usually working and the system around it is not. Before we condemn a blower, we look at the whole path the air has to take, because a motor rated for a great deal of air will still move almost none of it through a crushed transition or a damper that no longer opens.

Weak extraction with a healthy motor

Four things account for most of it. Duct that necks down from a large round outlet to a smaller rectangular run loses far more than the size difference suggests. Flexible duct with sags in it behaves like a series of traps. Grease that has built up on a blower wheel unbalances it and destroys its ability to throw air, which is why a wheel that looks merely dirty can cost you half the system’s output. And a wall or roof cap whose damper only lifts an inch will choke everything upstream of it.

We check the damper first because it is free to check and because on the coast it is the part most likely to have failed. Salt air seizes the hinge pins on exterior caps, and a flap that used to swing now lifts a little and drops back against the airflow. In houses within sight of the water we also see the opposite complaint: a damper corroded into the open position, which lets humid outside air and insects straight back down the duct.

Remote blowers on the coast

A remote or in-line blower mounted in an attic or on a roof solves a noise problem and creates an exposure problem. That housing sits in salt-laden air year round, and the motor’s bearings and the wheel’s balance weights are the first casualties. The symptom people describe is a rumble that gets worse over a season, or a vibration that carries through the cabinetry into the room. By then the wheel usually needs replacing along with the motor.

Make-up air and the tight-house problem

Newer construction in the county is built far tighter than a 1930s bungalow. When a high-capacity blower runs in a sealed house, the air it removes has to come back in from somewhere, and if there is no dedicated make-up air path it comes back down whatever opening is easiest — often the ventilation the house was not designed to reverse. The symptoms are a hood that clearly underperforms its rating, a back-draft smell, and doors that pull hard.

That is not a repair in the usual sense; it is a diagnosis. Where a make-up air damper exists and has stopped opening, we can fix that. Where none was installed, we will tell you plainly rather than sell you a blower that will not change anything.

Downdraft systems

Downdraft units add a lift mechanism to everything above. The common faults are a drive belt or gear that has slipped, a limit switch that no longer confirms the top of travel, and a unit that stops part-way because grease has stiffened the guides. Cleaning and re-lubricating the travel path solves a fair number of these outright. The rest are a motor or switch replacement, quoted before the part is ordered.

Which duct — because there are two

This page is about one duct: the run that carries cooking air from the hood to a cap on the roof or the wall. That run, its transition, its damper and the blower that feeds it are ours to repair. The other ducting in a house — the supply and return that a furnace, a heat pump or an air handler breathes through — is not. We do not install it, alter it, clean it or quote it, and a hood that has been teed into a heating or cooling duct is a fault we will report rather than a job we will take. If the complaint is about a room that will not heat or cool, the trade you want is a mechanical contractor.

What we bring back

Extraction you can feel at the front edge of the cooking surface, a blower that runs without telling the whole house about it, and a damper that opens fully and closes fully. Written estimate first, flat diagnostic credited to the repair, and the same parts and labor warranty as the rest of the kitchen.