On another popular reef forum there is a thread titled "Cobalt neotherm heater just blew up!!! " You can read about others experience like yours..... A 21 page long thread.
I’m so sorry to hear this! I almost purchased one of those last night as our heater is acting funny. I ended up canceling and ordered an Eheim 125 watt.
Also, to further bash my neotherm I bought a finnex to replace it and found the temp stays way more consistent then my neotherm did.. Just another thing to add to the list..