How often do you replace a heater?

Ive been in the process of making my tank more stable, and the one thing i cannot master yet is my temp, ill set my heater at 78 and it will be 80 in my tank and the heater is still running? something cant be right, ive had it for about 10 months now, is it time to get a new one? are these similar to lights? over time they just go? how often do your recommend changing them? or what is a good one for me to switch to that will be more stable?

 

I know heaters and the thermometers in them can be unreliable. You have said you are trying to get things a little more stable, have you looked into a controller? They can shut off the power to a heater to keep the tank at a more stable temp, and also perform many other tasks to aid with keeping the tank going.

 

I actually have been looking at them, right now im just debating on which one would be better for me, ive got a calcium reactor on the way, and id like to use the controller to control the PH to eliminate equipment, but just not sure which is the best one for the buck :-/ i know they make heaters with controllers seperate, but i just havent jumped on anything i liked yet..

 

I've been looking at the reefkeeper line. I think this is the way I'm gonna go. But hopefully someone with some more experience can chime in and give us a better idea of what's out there.