Thermostat not equal to the thermometer

[Vesper]

Ok so...before I used to use just a dimmer, but I went ahead about a thermostat that I've seen some people suggest. I bought some of the prob thermometers to double check the temperature.
The gauge on the thermostat says 78, the gauge on the thermometer says 90. It feels warmer then 78. And the thermostat hasn't moved up at all. I've got it set for 90, but it's just not getting up there according to his gauge.

For right now I unplugged the thermostat, worrying that it's trying to push the UTH up higher when it doesn't need to. My mate will be here all day to monitor temperatures, so she can adjust it if it gets too warm, but right now even without the thermostat it's hanging at 90. Anyone have any suggestions or problem like this before? I'm using/trying to use one of these: http://www.amazon.com/Hydrofarm-MTPR...dp/B000NZZG3S/

[The Serpent Merchant]

Where are your probes (both the thermostat and thermometer)?

the Hydrofarm isn't very accurate at all, that combined with the inaccuracy of cheap digital thermometers and you can get some pretty big discrepancies.

[PitOnTheProwl]

Location of both probes?
I never trust the numbers on the sticker at all

[Vesper]

Both of them are directly in the middle of the hot side, on the ground. I've got just about an inch of space between them so they don't touch each other and something effects it that way.

[Kaorte]

Are they on top or under the substrate? Where is the thermostat probe? I would move the thermostat probe to the outside of the cage (if you haven't already) and then adjust it until your thermometer in the tank reads about 90*.

[Vesper]

At the moment, I don't even have the thermostat on. The thermometer is hanging at 90 without it. Although, I know as it gets colder it won't. And they're both at the bottom.

[The Serpent Merchant]

What type of thermometer are you using, are there any other heat sources in the cage? I would question the thermometer readings.

[Kaorte]

What kind of heat mat are you using? It should be getting a lot hotter than 90º on its own.

[Vesper]

just an Ultratherm UTH heater is being used for heat. Nothing else. I'm not sure what kind of thermometer I've got. I don't see a name on it and I've already tossed the packaging.

[kitedemon]

It sounds like there are three things the first being ultratherms are self regulated to not get over 100º in an 80º room ambient temp. They in cooler rooms will not even reach this.

The hydrofarms are very very poor accuracy they are supposed to be with in 2ºC of correct (about 4ºF up or down from correct) long story but I have a number that I have been paid to evaluate. I think there is 3 in the first batch and 6 in the second. 3 of them are beyond the 4º mark from correct. They all read high ranging from 1.3ºF to 5.9ºF from correct. There is likely an error with the T-stat.

Digital thermometers come it two flavours cheap and accurate. Most cheap (sub 100$) have an accuracy of +/-2ºF for correct and with age this can decline more.

It is possible your thermometer is faulty or that is is incorrect one direction say 2º low and the hydrofarm is 4º high that would mean the hydrofarm set to 90 is actually 86º if the thermometer is 2º low 86º would read as 84º that is if everything is in the specs! It is easy for both to be outside specs too.

It sounds like both are an issue to me Personally I would suggest if you choose a hydrofarm a correct reliable thermometer (Traceable with less than 1ºF +/- error) is a must. Sadly the price of such a tool is more than the savings on the thermostat compared to a better reptile specific t-stat.