Check roof ventilation - suspected incorrect connection

Hello,

I would like to check our roof ventilation. I suspect that it is not functioning correctly.
My plan:
I would place a smoke bomb from the inspection shaft into the pipe leading to our house and seal it from the back to see if smoke rises through the roof ventilation.
I am looking for the right product for this. I only find parts that heat up or produce toxic smoke.

What should one search for?

Cheaper than the following fire brigade deployment would be to simply hire a drain cleaner to push a camera through there

A camera will find nothing in the pipe - I have had the impression since https://www.hausbau-forum.de/threads/ablauf-wc-irgendetwas-stimmt-nicht.36509/ that your plumber simply has a misunderstanding about the spring rigidity of air columns. With roof vents, there is also a wind pressure problem - possibly the pipe ends just too short above the roof ...

Cheaper than the following fire department operation would be to simply hire a drain cleaner to push a camera through there

Good point about the fire department. The devices I've seen so far, in my opinion, produce too little smoke to be visible at all. But of course, they could also produce a lot of smoke and cause problems.

The point is that we have already been inside the pipe with the camera. We have checked maybe 30 percent of the entire line. No defects were visible there.

Therefore, the question regarding the ventilation. For me, that can only still be the problem.

A camera will find nothing in the pipe - I have had the impression for some time now from https://www.hausbau-forum.de/threads/ablauf-wc-irgendetwas-stimmt-nicht.36509/ that your plumber simply has a problem understanding the spring stiffness of air columns. With roof vents, there is also a wind pressure issue - maybe the pipe just ends too short above the roof ...

11ant, I sometimes have trouble assessing your irony and statements. We have a vent pan on the roof. Adjacent to it is a photovoltaic system (not above it). Could this cause problems?

11ant, I sometimes find it hard to gauge your irony and statements.

There was no irony at all. It is a factual (and I suspect also the original) reason that many installers simply do not have the topic "physics" in their toolbox. Are we actually talking about the same pipe in both threads?

We have a vent pan on the roof.

That is usually quite a stubby matter and does not necessarily have to match the wind conditions on your roof.

Directly adjacent to it is a photovoltaic system (not above it).

No, in my assessment its proximity is practically irrelevant.