I have 3 Eheim Jager heaters in my sump which are 7 years old. They are 200watts each and I just finished cleaning and testing them. They test just fine.
I bought them new and they have never been submerged past the minimum/maximun line.
I tested them tonight and all are working just fine.
Key to keeping them new is to never submerge them past the min/max line on the head.
I keep my heaters vertical in my sump
