You have an electrical project that may become a HVAC project. It will be necessary to test whether the fan control in the vicinity of the cooktop is supplying power to the blower at the roof. If not, then the problem is with the control. If so, then the motor and/or the entire blower assembly will need to be replaced.

I can't tell you details of testing, as that might generate pages of if/then instructions. Generally, you wouldl need to determine whether the motor is induction type and essentially is connected by a pair of wires (conductors) in addition to a ground wire, or by a higher number of wires. In the former case, the motor might be replaced with one from, for example, Broan/Best, or even from Thermador. In the latter case the motor might have a more complex or switched control system which might be less easily replaced. There are so many options that refinement will require you to play detective or hire someone electrical who can perform this task.

Looking up this model reveals that it uses a separate control and separate remote blower, connected by 5 wires. See https://www.manualslib.com/manual/654617/Thermador-Vch36.html?page=2#manual. This will make evaluation slightly more difficult, but should not challenge an electrician in determining whether power is getting to the roof motor. The diagram suggests that the control is merely a switch applying 120 Vac to one or another of the motor wires.

Whether your particular remote blower is replaceable or not by a unit that uses the same control will require some further work on your part. Complete replacement of the control and blower is possible, but details of control adaptation cannot be guessed at without more information.

Here is the blower installation guide: https://media3.bsh-group.com/Documents/5060008385_A.pdf

AJMadison has some information if you know which of the three blower sizes you have.

I would suggest reviewing hood literature here and evaluate whether a hood upgrade would be appropriate.

Thank you!
We have had it evaluated a few different times and the end result is we need a blower replacement. Now I’m not sure how to identify which blower size we currently have?

We have a custom built hood and would hate to have to start over.

Can you provide a photo of the hood shell that your insert is inside of?

Can you measure the duct diameter?

Would you measure the hood entry aperture dimensions?

Did I correctly perceive that the hood intake is mesh, not baffles?

Modern-Aire, among others, could build an insert that fits your hood shell dimensions, if necessary.

As for blower size, we can estimate on the basis of the entry aperture size what flow rate you should strive for and hence what size blower to obtain. You would likely have to swap the four-position switch control with a variable-type motor control, easily obtained from an electrical distributor or supplied with the replacement blower assembly.

Hood

I’m sorry. What is aperture dimensions? Thank you!

This is the roof vent

The Wolf / Broan roof units in the 1000 CFM and up sizes should be able to replace this blower, but I can only guess from here.

The entry aperture is the area at the base of the hood through which air flows toward the hood filter system, such as baffles, sometimes mesh. Insufficient air velocity at this level can lead to cooking plume spillage. (Spillage is cooking effluent that entered the hood but was able to escape. This differs from uncaptured plume due to an insufficiently large hood entry aperture.)

Please review the first dozen pages of the Greenheck guide available here for insight into what your hood is trying to approximate in a residential setting: https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf

Is there any filtering up inside the hood? The photo doesn't reveal what it is. The filtering also provides the required firestop.

Yes we took the filters out bc we are trying to repair.

The motor on the blower in the roof vent is done. So do we get a new roof vent that is a Broan/wolf?

Do you think this will work as a replacement?

First, Wolf uses/used some Broan/NuTone blowers. I have one. We do not know if additional requirements are imposed by Wolf for the blowers they obtain from Broan. I am only familiar with the 1500 CFM (zero static pressure) Wolf roof blower. I am not familiar with Vent-a-Hood roof blowers.

So what is your intake aperture area or its dimensions?

What diameter is your duct and how long is it?

Please describe your make-up air system.

Are you OK with changing your blower control?