Trouble having enough heat

[Bogertophis]

Ahh perfect I understand, I'll take some of the substrate over the uth off and leave i in the rest of the tank, it makes sense he'll be able to be close of the uth !
Thanks !

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That's exactly right- that too much substrate over the UTH prevents the warmth from rising (plus it can make the UTH fail if it overheats as a result).

Also, UTH are not meant to be used vertically- first, it's not efficient- heat rises up & out- but also may cause it to fail?