Post pics of the original tstat wires and the Nest wiring you
connected.Do you have a heat pump, or a/c with gas heat system, or is it
a AC only system?
DAT and SRTN must be their data link. You might be able to run it in 24v
mode but will lose the data link features of the system. You might want
to call waterfurnace and ask them the pros and cons of not having the
communication with their thermostat...
Do you have pics of the existing wires on your t-stat?Their website
shows a few tstats that look like they were rebranded with their logo so
they must be using standard wiring.
You post pics on here by clicking the camera icon inside the chat text
box.Do you have AC and Gas heat furnace, or is this a Heat pump with
emergency heat?If its a Heat pump you normally have a O/B wire
connection.
Go to the nest and see if it says it's connected to wifi network. If not
then you have to go to the settings and connect to the wifi again. Maybe
the wifi network name or password was changed and they did not tell the
nest the new info.