Some things you can look at yourself before calling an engineer out to repair the product here is some of them.
As a general rule these are mostly all working on the same principal and using a system that is known as "falling air refrigeration". Basically an evaporator at the back of the cabinet exchanges heat for cold on the outside of the unit and the plate gets cold, the cold air then falls off the plate and slowly lowers the temperature in the fridge cavity.
How a "self defrosting" system works using this principal is that every now and then the appliance cycles and the ice formed by condensation on the plate, or back wall, liquefies and runs down to a defrost channel. It is with this part that problems happen.
Tiny bits of foodstuff or dust slowly clogs that defrost channel for the water to run away and you see water in the fridge. There is, basically a hole in the centre of the defrost pan it is this small tube that gets blocked and water can no longer drain away as it should and then you get water in the fridge. Easy to cure, just poke a bit of flexible wire down the drain hole and you've fixed it!
Never, ever defrost a fridge or freezer with anything made from metal EVER!
If you pierce the plate (or evaporator) quite often it cannot be replaced and more often than not it is too expensive too replace. The other thing is that if you do this you are on your own no manufacturer or insurer's warranty covers this as it is blatant customer misuse and it tells you so in your instructions.
Frost free is a term sometimes misused as it is used in reference to a falling air fridge. However generally within the industry it is meant to refer to a "blown air" refrigeration system. What this means is that instead of having an evaporator which air falls over it is actively blown by a fan into the unit. This has the effect of allowing for a "no-frost" or "frost free" freezer and a more stable internal temperature.
Firdge freezers that are frost free often use the "falling air" principal described above to keep the cost of the unit down but you can get "blown air fridges as well.
Blown air has several advantages bar negating the need to defrost the machine like the internal temperature is more even and, when teh door is opened, because the cold air is being forced the temperature recovers a lot faster than simply waiting on gravity to do its job.
With blown air the one thing to be careful of is not to pack the freezer or fridge too full as the air must be able circulate for the machine to operate correctly.
Common problems are defrost thermostats, fan motors and defrost heaters and, increasingly with modern machines, PCB failures. Now most machines are regulated not by old thermostats but using thermistors and electronics to control the machines.
Frost free machines are pretty complex things in many cases and we do not recommend anyone inexperienced try to repair.
Not many customers realise this but by the time you have noticed your fridge or freezer is defrosting you have lost the food in it! So make the most of it and throw a party or have a slap-up meal, you may as well or the food is going I the bin!
Food, when frozen, has to be maintained at -18˚C or thereabouts but this has to be the average temperature. If the food starts to go soft this means that the temperature has risen above this. Now, without getting too technical, when food is stored it degrades slowly by bacteria breeding and eating it away, that's why food goes off. But it all degrades sooner or later and the purpose of refrigeration is to slow that degradation down so as to make it as slow as possible and, when frozen, this is critical for hygiene. Once the food temperature rises and it starts to degrade then this degradation cannot be undone and also why once defrosted it cannot be re-frozen, unless it was fresh and is cooked first then re-frozen as this kills the bacteria. This is also why food cannot be kept forever in a freezer and it will eventually go off.
Our advice is this, if your refrigerator or freezer fails call an engineer, you'll probably need him.
Other than these faults call an engineer.