The Collaborative International Dictionary of English v.0.48:

Thermotherapy \Ther`mo*ther"a*py\, n. [Thermo- + therapy.]
   (Med.)
   Treatment of disease by heat, esp. by hot air.
   [Webster 1913 Suppl.] Thermotic

WordNet (r) 3.0 (2006):

thermotherapy
    n 1: the use of heat to treat a disease or disorder; heating
         pads or hot compresses or hot-water bottles are used to
         promote circulation in peripheral vascular disease or to
         relax tense muscles