When you buy almost any item (other than 'short life' things like batteries and windscreen wipers) and a fault occurs WITHIN 6 YEARS from the date of purchase, you have the legal right to demand a repair or replacement (but not a refund) if the problem is due to an INHERENT FAULT. (That means something which was actually wrong with the item at the date of purchase, such as the use of a poor quality component or poor workmanship).
For the first 6 MONTHS after purchase there's an automatic assumption (unless there's clear evidence to the contrary) that any malfunction must be due to an inherent fault. For the remainder of the 6 year period the purchaser must show that the most likely cause of the equipment failure was an inherent fault.
However the legal right to a repair or replacement comes about through the contractual relationship between the retailer and the customer. (i.e. any claim must be made against the RETAILER, not the manufacturer). The manufacturer is under no obligation whatsoever (to the purchaser) even if the item develops a fault on the day after purchase. (It's the retailer who is obliged to provide a remedy. It's then up to the retailer to claim against the manufacturer). A guarantee is a 'gift' from the manufacturer and is completely separate to your statutory rights.
So in order to make a claim for a repair or replacement you need to be able to show that the most likely cause of the problem was an inherent fault. (Sometimes simply challenging the retailer to suggest any alternative cause can be sufficient for this). Your main problem though would seem to be in the definition of a 'retailer'. You purchased the freezer from the builder, so it seems likely that the law would regard the builder as the relevant retailer. However I wouldn't be at all surprised if the builder tried to pass your complaint onto whichever company they had purchased the freezer from.
Chris