Elite heater?
 

i just replaced my heater about a week ago set the temp to 79 and now its stuck at 76 and wont go back.

Since it's a new heater, I would take it back to the store and exchange it. I would look at other brands available.

If the store gives you a hassle, you could try contacting the manufacturer at www.hagen.com

I bought an Elite heater recently and I believe they have a lifetime guarantee.

Thanks ill try tomorrow.

if you do trade it in for a new one, dont get top fin whatever you do, they do the opposite from not working, they work to much. Top fin over heat your tank to sometimes 100 degrees farienheigt. Im not sure about elite but im using an All GLass aquarium heater and its great, no temerature fluctuations.

Elite Heaters
 

I woke this morning to find all my fish dead due to my elite heater malfunctioning. The tank temp was 104 degrees Fahrenheit. I cant believe they don't have a cut off on the dam things. Max temp shown on the heater is 32 Celsius. :-(