Brake Pressure Sensor

[lsmithy]

Hi,

New member and very noob mechanic here...

I recently started having Stop/Start lights on my VW Polo SE TSI pretty much most days.
One time driving to Silverstone (of all places) I had an error saying 'Brake Servo Restricted' which instantly went away.
The other day the Brake Servo error came on and stayed on whilst on the motorway, did some googling and could have been the brake pressure sensor.
Felt brave and ordered a new one off Amazon and fitted it, however now when driving away my brakes are either really super light or extremely heavy and unable to use
Am I missing a trick, should I have done something other than just taking the sensor out and fitting a new one?

Thanks for any help!