We improved our high-latitude ionospheric model by including thermal conduction and diffusion-thermal heat flow terms in the ion energy equation so that we could study the ion temperature variations in the daytime high-latitude F layer in a region poleward of the auroral oval for steady state conditions at local noon. From our study we found that (1) The variation of Ti with solar cycle, season, and geomagnetic activity closely follows the Tn variation. The general trend is for higher temperatures in summer than in winter, at solar maximum than at solar minimum, and for active magnetic conditions than for quite conditions. However, Ti changes by less than 600 ¿K over the range of conditions considered; (2) Meridional electric fields act to heat the ion gas and electric fields greater than 40 mV m-1 can cause a larger Ti change than that due to solar cycle, seasonal, and geomagnetic activity variations; (3) In the presence of meridional electric fields, there is an upward flow of heat from the lower ionosphere that acts to raise Ti at high altitudes; (4) Zonal electric fields affect Ti indirectly through changes in the electron density, but the effect can be larger than that associated with solar cycle, seasonal, and geomagnetic activity variations; (5) Diffusion-thermal heat flow affects Ti by at most 500 ¿K; (6) Typically, Te has a much smaller effect on Ti at high latitudes than at middle and low latitudes.