I only seen this happen when ther no air flow under the tank ( i melted some flexwatt befoer) but I got lucky andwhen it melted it stopped owrking at the same time ) but anytime you set a glass tank onto a surface that down not have a opening under it ( like a coin ot 2 you need to set it on something. I have in the pass used lego blocks on their side ( a couple of thme ) to allow air flow) and i even used small strips of wood anything that will give you the space ot let air flow under helps. and if on carpet a trickto prevent the carpet from getting burnt is as thin sheet of plywood. ( panellng) with some thing ot lift for air flow. this prevent the carpet from melting andgives a little better chance of the uth from failing ( seem like carpet will insulate the uth and cause it to run hotter .