Reignited, temperature turned to carbon old item (5)
I believe the answer is:
relic
'old item' is the definition.
'relic' can be an answer for 'item' (I have seen 'antique item' mean 'relic' so perhaps 'item' could also mean 'relic'). I am not sure about the 'old' bit.
'reignited temperature turned to carbon' is the wordplay.
'reignited temperature' becomes 'iler' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'turned' says the letters should be written backwards.
'to carbon' becomes 'C' (chemical symbol).
'iler' back-to-front is 'reli'.
'reli'+'c'='RELIC'
Can you help me to learn more?
(Other definitions for relic that I've seen before include "Venerated memento" , "Survival from earlier times" , "Survival from an earlier time" , "Surviving artefact" , "One interestingly old" .)