ACT-210 Thermostat problem (?)

[littlemay]

So i've had my ACT-210 Thermostat hooked up to a 60 watt heat emitter for around two months now without any issues; consistently kept the heat gradient around 32 degrees hot end and 23 degrees cool end (all temps checked with a temp gun). Anyway this morning i woke up and found the basking ledge to be around 27 degrees, i could easily lay my hand flat on the heat emitter without a chance of burning myself; it was only just warm. Initially i thought the heat emitter may have blown so i cranked up the temp setting on the thermostat to be sure. The temperature went back up to around 30 so it clearly wasn't the heat emitter. Anyway, after a little while the temps began to drop again back down to 27, so i turned up the temperature setting again and again same thing, the temperature went up and then after about 15 minutes began to drop off again. The temps were checked on both my thermometer and temp gun so that's not the issue. Any one have any ideas on what could be going on here? Starting to suspect the ACT-210 could be malfunctioning...

 

[Wally]

Could your room temp be influencing the thermostat?

 

[littlemay]

I did think of that as it has been rather hot recently, however if this was the case i would have thought that i would have seen evidence of it at other times as well...? I check the temps several times a day and while they might fluctuate a degree or so they have never dropped off like this before.