Second job when you buy a Xantia Haynes manual . ..... . . ...
Search on 'frenchcarforum.co.uk' to find out how you actually change the glow plugs and print this page. Get a Prittstick (or similar) and stick the information to the space in the Haynes Manual (another printing error I expect) where this information should have been printed.
All you need to do now is get your self some "bendable" spanners, 4 plugs, something to protect your hand skin, and approximately 5 hours if it's your first time and 4 hours and 56 minutes if it's your second time (like me).
PS. To all you clever buggers who can do the job in an hour or so, please don't pick on me as I can't fight back with these swollen and cut knuckles