Chaps -Resurrecting this thread as I've encountered the same problem. we've had the 'boot open' warning on DIS for several weeks but thought it was a switch issue and didn't realise the boot light was also staying on. Came home from holiday and car battery completedly flat. Put a new battery on and then noticed the alarm light in the door is not operating. Alarm went off this evening and it's only then I noticed the boot light was on with the boot shut. So it's either always been on or there was a on/off episode to trigger the voltage drop and alarm.
I've changed the boot solenoid several months ago but reading the above I need to interrogate the lock assemby? Is the microswitch in the lock assembly and is it easy to change or is is better buying a complete unit? Any pics/diagram would be useful.