A noun in the Qenya Lexicon of the 1910s glossed “boil” under the early root ᴱ√PUŘU [PUÐU] “consume by fire” (QL/75). Its stem form was pust-, so presumably ancient ðt became st.
Early Quenya
wele-
verb. to boil, bubble
pus
noun. boil
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A verb appearing as ᴱQ. ’wele- “it boils, bubbles” in the Qenya Lexicon of the 1910s under the early root {ᴱ√WELE >>} ᴱ√GWELE (QL/103).
Neo-Quenya: For purpose of Neo-Quenya, I would adapt this word as ᴺQ. vel- with the usual sound change initial w to v.