Just had three of my Marineland 400watt submersible heaters replace after six months of use due to bad seal, causing water to build up inside the tube. After a closer look, I found one of them with sign of black burn mark on the board. So I had all three replace for free (guaranteed for life just like it was printed on the box.) Got the replacements in; tested them all out and guest what… the same @#$% thing happen to all three. Water build up inside the tube. Wait before you say it was me, I hook up an old school heater to the outlet and it work fine, no issues at all… now I’ve used six Marineland 400watt submersible heaters and they are all bad….. Now I’m going back to the store to get three replacements for the replacements Marineland sent, if the second sets of replacement are bad as well, I’m done with Marineland period. And will tell them to send cash not #$%@#$ that don’t work….