There is a lot of confusion between what is a Warranty and what is a Guarantee. Trawling the Web has alllowed me to come up with the following, but others may disagree.
In many cases they can be considered similar in as such that they are both legal agreements that can be challenged in Law. The EU states a warranty is valid for 2 years but under English Law it is valid for 6 years.
In most retail products anything you buy comes with a guarantee that it will work for a period of time, or a repair or refund is offered by the seller. A guarantee therefore is giving you a contract that the item will work for a period of time after sale. A warranty is telling you that the item you have bought is to a particular standard and again will operate as defined for a period of time or will be replaced or repaired. You may have the option to increase this period of time by buying a warranty that basically extends the guarantee period. Basically an insurance Policy. There has been a lot of bad Press regarding extended warranties pushed on you by many retailers as they often extend the time period beyond the reasonable life of the product, so you are paying for something you are unlikely to use, and they are usually very expensive per se.
Basically as far as caravans are concerned every piece of 3rd Party equipment included will come with its own guarantee from the manufacturer. The manufacturer will usually also give a warranty with the caravan stating that it has been built to a certain standard, either CE or NCC and they promise to repair or replace any item not satisfactory within a period of time, and often add a proviso that this is dependent on certain conditions being met, usually an approved annual service. For example if your fridge packs up within the guarantee period, then a replacement will probably be supplied by the fridge manufacturer, under guarantee to the dealer, who will fit it for you. However, if you have a damp problem within the warranty time period and have not met the servicing requirements, then the manufacturer may try to renage on his responsibilities by stating you failed to meet the conditions written in the warranty.
Neither a warranty or guarantee has any adverse effect on your rights under the Sale of Goods Act, however it is usually obviously much easier and simpler to get satisfaction without going that far. If you ever wish to challenge a warranty rejection then you need to ensure you have all the relevant documentation, keep copies of all letters, emails etc and if possible record all telephone conversations. Then, although not always necessary, get a lawyer who will write to the manufacturer/dealer stating the base of the claim, and set out what action will be taken in the event of satisfaction not being received. No manufacturer or dealer really wishes to go to a public Court so there is a good chance a settlement can be reached between you.
What is boils down to is really what document you receive when you purchase a new caravan. You need to read it carefully because as you have accepted the van, you have basically accepted what is stated on that document as part of the Contract between you and the seller. Although you can use the S of G Act as a final recourse, that will be time consuming and possibly expensive, if you do not win.
The fact that all manufacturers insist on an annual service being completed by an 'approved' establishment in order to maintain the Warranty, is of course a bit of a 'smoke and mirrors' trick. To follow an 'approved' service schedule that does not include the very equipment checks required to maintain the warranty is confirming that manufacturers and dealers feel this is just an easy way to make extra money. I always laugh when I see that I have been charged for someone to 'check my road lights are working'. I check these every time I set off. Probably the main value of the service is the damp check, although it is an expensive way to get one done.
However, it would be very interesting to see it tested in a Court of Law whether any manufacturer could renage on his obligations by arguing the gas burner in a fridge had not been cleaned annually, although the 'approved' service schedule had been followed.