Clear all messages on iOS 8 Due to the effective. Power bug, my iMessage app CAN open, but if I scroll down to a particular conversation (the recipient name won't load without crashing) the app suddenly closes.
As well as fixing this I just want to clear my messages to save storage space.

Is there a way to clear all my messages without selecting and deleting them in the app?
Short of resetting or jail breaking your device, there's no fast way to do it.  But, maybe you can use the Message History option under the Messages app setting to your advantage.  Assuming you don't already have it set to 30 days, change Keep Messages and have iOS automatically get rid of a majority of your messages.  Then, you can proceed to delete the rest manually, which should be a lot less.