Along with the OS X 10.10.3 update, Apple issued Yosemite Recovery Update 1.0 to fix a few bugs and enhance the Recovery process for systems running OS X Yosemite. The update is available only through the App Store’s software update service, and while this service should only show software that has not been installed, for some people their systems are constantly showing this update as being available. This continues even after attempting to install the update multiple times.
The recovery update addresses your Mac’s hard drive’s setup, and it appears that in some circumstances, some hard drive configurations may hinder its ability to be applied correctly. Since the update cannot be downloaded manually, you have no option but to use the App Store for applying it, so if you run into this issue, then you have a couple of options for overcoming it:
If you have external hard drives attached to your Mac, especially if you are using cloning software to maintain a backup clone of your system, then disconnect them and see if the update will apply. While a clone is a likely culprit for this issue, other drives you have may also be at the root of the problem, so simply disconnect them all.
2. Disable FileVault
While the update should apply over a system running FileVault, Apple’s full-disk encryption technology has been an issue in the past for updates, and may be a contributing factor here. To disable FileVault, go to the Security system preferences and then click the option in the FileVault tab to do so. Authenticate, and then wait for the drive to be fully decrypted (this may take several hours to complete). After it is done, try reinstalling the Recovery Update from the App Store.