Ice build-up in a fridge can cause it to go warm up. As ice is an excellent insulator, this prevents the fridge from drawing out heat to keep the fridge cold.
Usually, ice build-up is from moisture that enters a fridge which eventually coos and start forming ice blocks.
The following reasons are usually the cause for ice-build-up:
Keep the door closed
The door may not be closing correctly due to a damaged door or broken seals.
A frequently opened door or a door left open for long periods can also cause ice build-up.
Damaged door seals
Check if the door seals have any cracks or broken pieces. Damaged door seals allow moisture to enter which speeds up ice build-up. Repair damaged seals with super-glue and replace perished seals.
Defrost not working
There may be an issue with your defrost timer, defrost sensor or defrost elements. A qualified technician should test this for you to find the cause.
The fridge thermostat could be faulty and not allowing the compressor to turn off.