gas safety

What are the obligations (if any) of a tourer dealer with regards to gas safety checks on vans they sell to the public? This question is in relation to a van i recently bought that on our first outing pumped gas fumes from the fridge into the van, tests by an independent expert revealed flue blocked with carbon, pipes from gas cylinder from bottle to appliance not changed for years, flame burning yellow instead of blue, fridge insecure in housing causing fridge to move about in transit, we are happy with the van itself, it is an old van and in general good condition but as newbies to caravanning  we accepted the dealers assurance that the fridge and other appliances were in full running order, having informed the dealer of all this they are saying that gas checks on tourers do not have to be done by "gas safe engineers and do not have to be issued with a "gas safe certificate " prior to sale, they are anxious to have the van back for repair but are indicating it not a good idea to get 3rd party involved, i have no confidence that they will repair the van competently but also i am concerned that should they be selling vans without proper gas checks, on the receipt they gave me they wrote "yes a gas check had been done", i am find ing it difficult to find online the exact infor re dealer obligations on gas checks on vans they sell, can anyone help with this please.