My baby is 8 weeks old my steriliser hasn't been sterilising his bottles properly is that harmful ??

You don't say what the problem is or how you know it is not working properly. The only thing a sterilizer does is to get hot. You can do the same thing with any pot on the stove if it's big enough. It's important to sterilize bottles because baby's immune system is not working normally at first. That is the same reason the tell you not to use honey before age 2. (I think they said 2. It's printed on the label.)