Is the stick-on black mat type?
I returned all mine.
Even a thermostat wouldn't stop it from trying to bake my snakes.
I went to the heat cable type.
I can regulate the zones much easier and it responds to the thermostat.
My first UTH cracked a 20L tank and melted the plastic frame.
Luckily, Iggy wasn't on the warm [HA!] side when it happened.