If you have cloth seats it should be possible to replace the seat heater pad, all be it at a price from the Vx parts catalogue. Replacement heat pads do however occasionally come up on ebay (seat pad or seat back) which is almost certainly the culprit if the seat has power and it's not something silly like a blown fuse. If your seats are leather then you have a problem as getting the heat pad out to replace without trashing the seat is difficult without advanced leather haberdashery skills. Most of the Vx dealers simply replace the whole affected seat cushion at exorbitant cost (had this done twice under Network Q warranty). Vauxhalls own electronic manual does state it’s possible to replace the pad separately on leather seats but in practice they won’t do it (most garages lack the above skills). If your seats are cloth I would give it a go, if their leather and you really want heat you have a bit of a problem as replacement cushions are ruinously expensive. If you go second hand it’s likely the driver’s seat heat pad(s) will also be kaput as its seems to be a very common Omega problem.