In Mand. and possibly in JBAmag. and CPA with metathesis as rḥt, but the latter is also a by-form of rˁt, q.v.
Unlike ḥmm which normally refers to natural heat, and šḥn "to be warm(ed)", this verb in its non-figurative senses would seem to refer to things heated by fire, and especially to boiling; for which see for example s.vv.
rtḥ, rtḥˀ n.m., rtḥyn n.m.pl.