I've actually already solved this problem, but as I couldn't find the solution online and had to go through a call with their support to resolve, and it's actually an easy fix, I thought I'd post it here so people can find it through search. So feel free to not reply 
I reset my Bosch smart thermostat, for reasons. Which went fine, but then I couldn't get my Smart TRVs to reconnect.
I tried resetting the TRVs using the method here :
For Homeowners - How to factory reset an eTRV - YouTube
No joy!
I dropped an email to Worcester Bosch support, and got a call back the next day, and they talked me through the procedure to fully reset it.
I reset my Bosch smart thermostat, for reasons. Which went fine, but then I couldn't get my Smart TRVs to reconnect.
I tried resetting the TRVs using the method here :
For Homeowners - How to factory reset an eTRV - YouTube
No joy!
I dropped an email to Worcester Bosch support, and got a call back the next day, and they talked me through the procedure to fully reset it.
- Remove a battery from the TRV
- Hold the O button
- Insert the battery again
- Keep holding the O button, after a few seconds it will start flashing orange
- Keep holding until the orange flashing stops, then release the button, and quickly press it again