Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Pelonis NTK15 heater, unsatisfactory operation

I bought a Pelonis NTK15 oscillating ceramic heater about 2 years ago. Ever since the first time I used it, the fan motor has started up very slowly and made odd noises while starting up. This would go on for about 15 to 20 seconds, then it would speed up and stop making the odd noise. During the 2 years I have owned it, this problem has slowly gotten worse. Now, it takes even longer to start up and never does get fully up to speed and never entirely stops making the odd noise, even after it has warmed up. I have cleaned the filter regularly and made sure there are no obstructions that could prevent proper operation, but nothing helps. It has gotten to the point where I am reluctant to use it at all, because I am afraid it might overheat or short out and possibly cause a fire. I would not recommend this heater to anyone. It never has worked properly and I feel it may be unsafe to use.