Blister under Descent MK1

I've had this watch for three years and the heart rate monitor light is always flashing. 

Today it went solid green, heated up real hot, and actually burned a blister into the top of my wrist. 

I logged in to the online dashboard and set the heart rate monitor to "off".

Rebooted the watch, and still solid green light with rapid heat build up.

It's shut off now until I figure out how to fix it. 

Any ideas?