Well my heater malfunctioned and the temp reached about 90. I have a hammer coral and as a result, the soft tentacles all came off and all that remains is the skeleton. Is there still hope or is it completely dead?
I thought I had a malfunctioned heater in my sump when one of them wouldn't turn off and the other would on the other end. Turns out that water flow has a cooling effect and even though your temp may read ok the heater is being cooled by the flow. I moved it to another chamber in my sump where the water flow was less and it worked perfect. So I put it back into the other chamber but at a lower temp.
Point I'm trying to make is that while the heater may have malfunctioned in your case it should be known that this to can cause the illusion of a broken heater.
I'm also curious as to what brand it was. Would love to read the reviews on it.