Whats going on tank not heating?

[a123andpoof]

So I just bought a new heater to put in this tank
http://www.walmart.com/ip/Tetra-Glow...-Pets/12177652

The temp is not going up! I have the heater in 1 corner and the thermometer in the other. Its a glass one. I use the same heater in a 5 gallon with no problems. I can't figure out why I even have 2 heaters and the temp hasn't budged. Should I try putting the filter in to distribute the heat more? Does anyone have problems heating this tank? My room is like 66 but all my other tanks stay at an acceptable temp and usually I have no problem heating smaller tanks so I don't know whats going on. Any ideas and or suggestions?

[Mo]

Cold the heater or the thermometer be malfunctioning? First I would try a new thermometer, and if that doesn't work, then buy a new heater.

[a123andpoof]

No the heaters are no malfunctioning as the one was in another tank and working just fine. I tried two thermometers.