Pokorny gives another root for Greek pur, English fire: *pew@r-, *pur (gen. *pu-n-es). Unfortunately, Latin lacks a word meaning fire that uses this root; it uses ignis (cf. Skt agni) and Greek lacks an adjective pure from the other root, but I note that Latin's sister, Oscan, has pir 'fire', so maybe the could take of purifying fire. In Sanskrit paavana 'purifying' is often used in conjunction with Soma 'the divine elixir' which is associated with the Sun, suurya.