hi,

One week ago my cpu idle temp was around 42 degrees C. This week it
has jumped to 52 degrees, while the case temp has remained at a
constant 35 degrees.

A week ago it only got to 52 dC under heavy load!

Why would this happen? The HSF is still on solidly & is running at the
same fan speed as when i bought it 18 months ago.

Is it possible the CPU is defective