Changing z offset for bltouch have no effect

Hello everyone hope you are all doing great ! This is my first post on the forum (hopefully in the future I will make contributions rather then questions ). So I have a Tevo tornado with an E3D v6, I am trying to install a blrouch on it but I am having some troubles. First I am using an endstop switch to home the z axis and not the bltouch (because it fall outside the bed once x and y are homed). Everything seems to work fine but when I tried a first print I noticed that the head of is too close to the bed and it is not able to extrude any plastic. What I did and what is happening:

1. Home all axis
2. Move the bltouch to any location above the bed.
3. G30 (bltouch probes in place)
4. G0 Z0 (head goes down but hits the bed)
5. I try using M851 Zx.xx to change the z
6. M503 to check the it did change indeed

If I repeat the above the head still bumps into the bed no matter what value the z offset is

Any idea what could be happening ?

Thank you