I had the same problem with my KGU3220GB for the last 3 years. You can remove the rear panel of the freezer just by pulling it out. The panel has a fan with a wire which will unplug from the top right rear.
The ice build up is due to the defrost cycle not working. Ice will build up in the freezer, stopping cold air circulating to the fridge. Then the fridge-freezer decides to start beeping and totally shut down.
I've given up counting the numner of times I've had to manually defrost the freezer- probably every 2/3 mnths.
Bought the Bosch new from John Lewis and 2 mnths later I lost all my food (£200+) when the fridge freezer decided to warm up (I hadn't noticed the freezer icing up). The Bosch repair engineer said the fridge-freezer was perfect, but there wasn't enough air circulating behind the unit as it was sited in a corner! John Lewis washed their hands of it and expected me to take 2/3 days off work waiting for Bosch service engineers to hear the same siting bollox.
I've now just bought a liebherr fridge. Spoke to the liebherr service guy about the Bosch. He said the "siting" expalnation was a fob off - there was more than enough clearance for air circulation. The fault is with the PCB (printed circuit board) behind the digital temp display. Bosch pcb's are notoriously unreliabable. A new one costs ~£120- £150 + fitting.
I had a go at removing the pcb, but could work out how to remove the top panel to get to it??
Overall, I will never buy any Bosch and any white goods again from Peter Jones/Jone Lewis. I'm a tradesman too and have since switched to buying Hitachi powertools too.
Iain
March 2006