What does the HH mean on a Pampered Chef digital thermometer?

I have a PC thermometer/timer that I love. We were frying a turkey and the display started showing an "HH" for the Probe temperature. Any suggestions on what may be wrong or how to reset it? Any help is greatly appreciated!

Can you use a meat thermometer in meat that is being deep fried?

Frying a turkey and I’d like to cook it to temp instead of going to time, checking temp, and trial and error until it is cooked (or overcooked), but I’m not sure if it is safe/effective to use a meat thermometer while deep frying. Help? Tips?