The EHIC is valid in all EEA coutries, plus Switzerland. The European Economic Area (EEA) is made up of the 27 EU countries, plus Iceland, Liechtenstein and Norway.
Turkey is not in the EEA
Geographically, Turkey (or, more accurately, most of it) isn't in Europe - it's in Asia - but most (and probably all) insurance companies include Turkey within their definition of 'Europe'. (They also include the Canary Islands, which are geographically African, and Cyprus, which is geographically Asian - even though it's in the EU!).