訓 わ(く),わ(かす) ・ 音 フツ
漢越音: phí
The water radical 氵 gives the meaning and 弗 the sound: water bubbling as it boils. Sino-Vietnamese phí, as in phí điểm (boiling point).
Stroke data: KanjiVG (CC BY-SA 3.0) — kanjivg.tagaini.net
お風呂が沸いた。 (おふろがわいた)
The bath is ready (hot).