OllieB, I am sorry about your issue, however we can try to perform some troubleshooting. That way we will know if replacing the NUC would be necessary.
Since you have BIOS version 0023, we can try to reinstall the original BIOS v0018.You would need to do this using the BIOS recovery method. http://www.intel.com/support/motherboards/desktop/sb/CS-034524.htm
Clear CMOS might help also, but on NUCs is not necessary to take out the battery. Please check the following information on how you should do it.
If this behavior persists please contact our Warranty Department so they can help you replacing your product http://www.intel.com/p/en_US/support/contactsupport
Please take into consideration that if the product was purchased less than 1 month ago, you would need to RMA your NUC through the place of purchase.
I recommend you to update the BIOS of the new NUC, but please install each BIOS version available.