taffyboy

Hi, can anyone help me with my 2002 WRX STI Prodrive which has developed a fault. The fault is reading "Oxygen sensor heater" (bank 1 sensor 1) and the fault code is P0031. Has anyone else had this problem if so where/ which sensor does this relate to with regards to its location and also does anyone know where the best place is to get a replacement - many thanks Taffyboy.