have a light on it looks like a resevour with a fan in it. We replaced the thermostat it was bad. And it looks like my expansion tank has a crack in it. I don't know if the computer can detect that and that is why my light is still on or what. It just kinda worries me, it gets up to tempetature real quick but does not overheat just stays at half way like normal. my water gets really hot inside there to where it is boiling is that supposed to do that.?? Does a tech need to reset my light to get it to go off maybe??