Bombeni, you should be able to get all your tanks working again if you want to. DavidOck gives good advice above. Sometimes there can be problems, but it doesn't mean you have to toss the whole thing, and buy tank after tank. If you could give a little more detail than the tank is fried or works half-assed, it might be easier to help you figure out what's going wrong. You should definitely not be seeing them "blaze fire"! Not sure what's going on with that.
If a tank works on one battery and not another, it's usually a sign that the centre post in the battery got pushed down too far. That can happen from over-tightening the tank, especially if one tank, or your charger, is a bit longer than another. Try what David says to (gently!) adjust the battery post.
After that, as he says, the coils in the tanks are replaceable. Just pop a new one in and you should be good to go. It could be that 20 watts is too much for those tanks, but I never go above 10, so maybe someone else can comment on that.
Most of them are iclears. The first time one glowed fire my son saw it and said hey those are cool they light up! I've seen two others light up/fry since then. at same time there's a horrible stench taste. I'd be afraid to use another one. One time the top of the 20 watt got real hot I figured it got damaged. I've been running it around 10 watts, both of them.