What caused my electric deep fryer to overcook violently? Last week, I was preparing dinner for my family. I didn't have much time, so I bought some frozen potato-balls to deep fry. Everything went well, I fried 2 or 3 batches without any problems, and also when I loaded the 4th batch nothing seemed out of the ordinary.

However, when the 4th batch was at it's third minute (cooking time was 4-5 minutes) the fryer suddenly started making a lot of noise. A lot more than normal. When I went to have a look, the oil was boiling very violently. I immediately pulled out the basket, expecting the boiling to stop, but only a second later I dropped the basket to pull out the plug ASAP, because I was afraid it would get worse.

I screamed at everyone to move away from the kitchen, because I didn't want anyone to get splashed with 200°C oil. Only a few seconds later, it turned out that we dodged a bullet there, because that's when the explosions started. Loud pop and bang sounds came from the fryer, and the oil shot upwards, all over the countertop. It continued doing so for over 15 minutes. Sometimes it would stop for 20-30 seconds, but then new "explosions" would follow. This continued for at least 15 minutes, but I only felt safe taking everything away 30 minutes later, because there was still an unusual noise coming from the fryer.

So... my question is: What caused this? 
I know adding water to hot oil is a recipe for disaster, because the water gets trapped under the (lighter) oil, preventing it from evaporating.
Also, this 4th batch were the last pieces of the bag, so it's certainly possible that there were still clumps of ice attached to some of the potato-balls. 

However... My issue with this explanation is: why did it bake without any sign of trouble for more than 3 minutes? I'd think that if you were to drop a small clump of ice in 200°C oil, it would get to boiling temperature in less than a few seconds? 

Knowing the cause of the accident is important to me, because I want to know if it is safe to use the device again. Because for all that I know, it also might have been a faulty thermocouple? Maybe it didn't give the right feedback to the heating circuit, causing the oil to overheat?

Anyone care to give some insight?

Thanks in advance!
As you cooked by batches the last one add brought much more water than usual because


it was the last portion of the pack and usually ice pieces are coming down as well
the frozen balls kept condensing water on them for all time you fried the first batches. 


Except if meantime you have discovered a malfunction of the fryer so that the T goes so high at the heating element to cause the oil to start fuming.