Thanks, and welcome to the TTN Community/Forum 
Dont know quite how (was tinkering vs being methodical in process as thought it was bricked) but by co-incidence I actually got it up and running, completed bootloader update and upated f/w about 10pm last night! Have had it on test last 24hrs and all being well it will get deployed in NWest UK next week
May be down to fact I think the Sentrius AP was updated on phone sometime over last week or so and also I removed/re-inserted batteries a few times last night before success and tried pairing with the device (could be seen in Bluetooth connections as a potential target) about 5 or 6 times with device rejecting pairing each time before I then went back in using the AP which saw it still in DFU mode but thankfully this time accepted the connection and immediately started the bootloader update then kicked in with the f/w update. I have another unit I need to get online over the weekend before the NWest trip and will be careful to track and note each step this time to see if it comes up ok. If there is anything significant will repost here, if all normal I will go silent