UTH or Thermometer Issues?

Just have a quick question: I have a Herpstat II regulating a ZooMed 10-20 gallon UTH on the bottom of a 20 long Zilla Critter cage (30"x12"x12"). I just use repti-carpet as a substrate, with sphagnum moss in some areas of the tank to up the humidity. I use something similar to the Accurite digital thermometer with the wired probe. I have the herpstat set at 92.1F, with the probe between the UTH and the bottom of the tank, but when I woke up this morning the thermometer was reading 96F (thermometer probe is under the substrate inside the tank). I used an IR temp gun to try and corrobarate the thermo, but I could only find a high spot of 92.3F.

Anyone have any ideas what could be happening?

Usually my husbandry is spot on: 91F hot spot, 79F cool side with an ambient around 81F most of the time.

Maybe the batteries in the thermo are getting low? Maybe the snake laying on the thermometer probe is offsetting the reading (not sure if that would even be possible)? Any thoughts would be appreciated.

Ok, maybe it wasn't so quick..

Could be low batteries. I have gotten wrong reading because of low batteries before.

You need to realize that the thermometers that we use in the hobby are cheap and inaccurate. Cheap thermometers have what is called error. Error is the amount off from the actual temperature that the thermometer reads and can still be "working properly" according to the thermometer manufacturer. Most are in the +/- 2-6 degrees F range so your thermometer could very easily be reading 96 even though the actual temperature is 92. Trust your herpstat. You payed a lot more for that than you did for your thermometer or temp gun (which are usually just as inaccurate as the thermometers) Herpstat probes are accurate to +/- 0.9 degrees F which makes them many times more accurate than anything else you have to measure temperature. Unfortunately accurate thermometers usually cost hundreds if not thousands of dollars so they are out of the reach of many hobbyists.

You can try replacing the batteries, low batteries will effect the readings of a digital thermometer. But as I said before cheap thermometers are inaccurate and their readings should be taken with a grain of salt.

You pose a good argument Aaron. It put me at ease. Thanks.