Help replacing front derailleur
As far as I can tell the 2015 Carrera Vulcan came with SRAM X4 all round. If the front derailleur is a Shimano unit it definitely was not original. I would guess the previous owner swapped it in. A Shimano unit will have 'Shimano' and 'Tourney' written on it. A picture of the derailleur added to you question will help us provide a good answer. 

In general SRAM and Shinano derailleurs and shifters are not compatible because they use a different cable pull ratio (how much cable is pulled to move the derailleur a certain amount). 

You options for replacement depend on what front shifter you have. If the shifter was also replaced with a Shimano unit you'll need a Shimano derailleur replacement. I'd avoid the Tourney range and upgrade slightly to something in Altus or Acera ranges. The exact model you want depends on if the the cable routing comes from the top or bottom of the frame. 

If the shifter is still a SRAM unit you the obvious choice for a replacement is a SRAM X4 unit as was originally fitted. I don't think SRAM makes these anymore but they are available from Ebay, Amazon etc.