When engine is running the brake pedal loses pressure and goes to the floor

Welcome to 2CarPros.

First, this vehicle isn't offered in the US so I have little technical information related to it. However, if the brake pedal is going to the floor, it is most likely the result of a faulty master cylinder. Over time, the plungers break down and allow fluid to bypass them. The level in the reservoir won't change because it isn't actually leaking. Without the power assist when engine is off, you aren't able to push it to the floor. With the assist, vacuum is doing the work and it goes to the floor. Note: With the engine off, press and hold pressure on the brake pedal. See if it slowly goes down. I bet it will.

Regardless, if there are no leaks and the reservoir is full, suspect a bad master cylinder.

Take a look through these links:

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Here is a link that shows how in general one is replaced.

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Let me know if this helps or if you have other questions.

Take care,
Joe