  We analyse the reheating in the modification of \nuMSM (Standard Model with
three right handed neutrinos with masses below the electroweak scale) where the
sterile neutrino providing the Dark Matter is generated in decays of the
additional inflaton field. We deduce that due to rather inefficient transfer of
energy from the inflaton to the Standard Model sector reheating tends to happen
at very low temperature, thus providing strict bounds on the coupling between
the inflaton and the Higgs particles. This in turn translates to the bound on
the inflaton mass, which appears to be very light 0.1 GeV <~ m_I <~ 10 GeV, or
slightly heavier then two Higgs masses 300 GeV <~ m_I <~ 1000 GeV.
