Autotune no longer works. Temp goes 20c over and errors.SOLVED

Okay folks,
I'm starting to think the old board isn't dead.
After rebuilding the hotend I decided to autotune the hotend again.
I issued,
M303 E0 S200 C8
and
M303 E0 S170 C8

Both times the temp climbed straight up to 220 and 190c respectively and the
pronterface came back with a temp too high error.

Any ideas what is happening? the temp is swinging a too much on the hotend and
I'd rather not have to adjust it by hand.


Many thanks,
Andrew