Never had any problems with Currys, after the 28 days they reserve the right to return the unit for repair under the manufacturers warranty but if you explain that the unit is important for your business/eduction use you may find that even after the 28 days they will still do an in-store exchange.
Currys are big enough to stand the cost of replacing units, they will send faulty units back to the manufacturer anyway.
If you are still within your 28 days just take up their offer.