I DONT THINK MY FISH HEATERS WORKING????? WHY?

ok so its a 25w little stick looking heater that snapsto the side of my tank. its plugged in and all, but when i look at it the on light isnt on, so i taake it out, adjust it, and put it back sumtimes it coms back, but goes out sometimes. im getting fish 2maro and it needto work. id go ask my dad but its 10 and i am "sleeping" and if he knew i was up, well i woodnt be getting no fishies