The e-series heaters are junk. I had one, it would not heat the water to the set temperature. I'd set it to 82, the thermometer on it would read 79, the backlight would be blue, and I could see the heating element coming on for a bit, then turning off. Was probably running a 20-30% duty cycle. I left it for a week, it continued doing the same damn thing. I replaced it with another one, same damn thing. Fluval was no help. So you have a heater that is clearly displaying the fact that it KNOWS the water is too cold, but it just isn't running its heating element.
I put my marineland heater back in, significantly less wattage, worked PERFECTLY. Temperature held as set.
That said, ANY heater is a disaster waiting to happen. The trick to averting it is redundancy. You get a heater and a temperature controller, you set the controller several degrees higher than the heater, and you occasionally check the temperature. If the temperature jumps up to the controller's setting, your heater got stuck on and needs to be replaced. You can also just use a quality controller with a titanium element, but I don't like the idea of cooking my fish because the cat knocked the temp probe out of the tank.
I want to see a GOOD solid-state heater on the market, like an e300 that doesn't suck.