Inability to feel temperature can have various causes, ranging in severity from 'worrying' to 'very serious'. Finding the true cause means ruling out or confirming each possibility – in other words, diagnosis.
Diagnosis is usually a complex process due to the sheer number of possible causes and related symptoms. In order to diagnose inability to feel temperature, we could:
Do you have difficulty in telling (feeling) the difference between hot and cold?
Possible responses:→ Don't know
→ A little difficulty / sometimes
→ Definitely / always