Not sure about the free service, but sounds a bit naughty. However under the sale of goods act any product sold must be fit for purpose. Clearly your bike isn't. It should work for a "reasonable" period. "Reasonable" is not defined in law, but a six months is not reasonable. The dealer has a duty to repair or replace the bike. Phone them and state the sale of goods act 1979. If they won't play ball then phone your local trading standards who will help you. If you bought the bike on finance then the supply of goods act 1973 applies which makes the HP company responsible Paul.