Temp gauge rising

[RickNotts]

Has anyone else had this problem?  The temp gauge reads just on the red when engine running at normal temp and at rest it reads about one third of the way up the gauge - ie not at cold.  It has gradually crept up to this state over several weeks.  I have changed the sender on the block but it's had no effect.  Any thoughts, gents?  Thanks.  Rick 
PS 1.9TiD car

[Saabman]

I'm not too clued up on the Diesel but is there not more than one temp sender unit? most modern cars have a couple at least to control different things by the ECU, I'd be tempted to plug it in to a decent diagnostic machine or Tech 2 and see what the live data is saying.