I was getting so crazy down temps on my X4D probe than just stuck on 3.8. I contacted Fishhawk and they told me to fill out a warranty form. My unit is definitely older than 2 years and didn't have the original receipt. They just needed the serial number. They said the thermistor failed and is unrepairable. In 2 days I received a FH400r probe at no cost! Those guys are the best and really stand by their products!