Ok after my thread this morning ref: low coolant levels, I topped it up, but its lost more water and the light came on again!!

Help!

What could cause this? Somthing simple like a split pipe? or Headgasket?

Look for puddles under the car. Could be a split pipe, a weak jubilee clip on the pipe(s) or a leaking radiator. Could also be the head gasket too....

To check for the latter look for oil in the coolant floating on the surface. Also check under the oil filler cap for white milky gunk.

Ultimately the only real way to check without taking the head off is a leakdown test. This is where they fill the cylinder with gas to see how much leaks out into the adjacent cylinder or to the outside world.

A garage should be able to do this.