Dodgy second hand motorhome

J and P Green

We have recently bought a second hand motorhome from a dealer.  We have had three trips that have all ended with engine problems with the engine warning light showing.  Our dealer refuses to give us our money back as a deposit on a brand new motorhome from
them. They tried to repair all the faults but we had to get it fixed in France as it broke down completely.  We spent one whole day of our holiday at a Peugeot main dealer while a new fuel ignition was replaced.  Although we have six months warranty, we have
lost faith in our motorhome.  The dealer is paying for this repair but won't let us buy a new one with the £29000 we paid for our second hand one.  Does any one know how we stand legally?