heater isn't heating

Did you turn the dial to a preset temp?.When it is below the required temp a light should come on to let you know it is getting the water to the temp you choose.
 
100w should be sufficient for a 29g tank in a room temperature environment.

first, check that it's getting power from the outlet.
second, check the thermostat.
third, check that the heater actually gets hot (you can do this by BRIEFLY removing the heater from the water after it's been on for a while, it will steam the water off.. be careful not to leave the heater out of the water for more than 5-10 seconds, as it can damage the element)

lastly, if all above is checked, get a new heater.
 
if you end up needing a new one, I suggest visisterm stealth heaters...

where is your thermometer in relation to the heater...if you do not have enough flow throughout the tank you may end up with some temp differences
 
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