Hi, I suspect you've found the correct sensor at Coastal Climate Control. Sensors need to be matched to the part they are designed to work with, to match the programming in the unit and in your case that is the Coastal Climate Control MKII/MK3 digital thermostat.
Check the connections at the display, then look at the distance from box to display, if there is solder/butt connector in there, like the sensor wire wasn't long enough to reach the display, check that as well.
A resistive/open /corroded connection will cause the error as well as an actual faulty sensor.
There 2 types of sensors.
NPC or PTC.
The thermostat only displays one (of three) dashes, which is not what the manual says is open probe. It also does not respond to the "Set" button when I tried to do a factory reset or other setting per the manual.
I'll call coastal in the AM. I suspect the thermostat unit itself is toast.