Yeah have a Spyder Robotics Herpstat for my thermostat. I have the temp set for 88 degrees, I just checked again and it is now at that temp so you are right it must just take time to warm up. I bought the flexwatt from AP prewired. First time using Flexwatt have always used other UTH so didn't know till now it takes a bit longer to warm up lol. Thanks for the reply!