Just drove my Elise (6 months old) to work on the warmest day we've had in weeks to discover it overheated! No warmth in the rad at all. Bit of a pain when it is also sleeting/snowing outside.
Superfast AA man (with big torch) has identified that the water tank is empty an we assume something has frozen/split and or popped off in the extreme temperatures here-it was parked outside in -15 degrees for a night.