I have this code:

In[1]:= H[u_] =    1/2 ((-2 + Erfc[-((5 u)/Sqrt[2])]) Log[        1 - 1/2 Erfc[-((5 u)/Sqrt[2])]] - (Erfc[-((5 u)/Sqrt[2])] -          Erfc[-((3 u)/Sqrt[2])]) Log[        1/2 (Erfc[-((5 u)/Sqrt[2])] -            Erfc[-((3 u)/Sqrt[2])])] - (Erfc[-((3 u)/Sqrt[2])] -          Erfc[-(u/Sqrt[2])]) Log[        1/2 (Erfc[-((3 u)/Sqrt[2])] - Erfc[-(u/Sqrt[2])])] -       Erfc[-(u/Sqrt[2])] Log[1/2 Erfc[-(u/Sqrt[2])]]);  In[2]:= H[2.1] // Log10 // N[#, 10] &  Out[2]= Indeterminate  In[3]:= H[Rationalize[2.1, 10^-10]] // Log10 // N[#, 10] &  Out[3]= -1.047657131 

However, when I do

In[4]:= Plot[(H[Rationalize[u, 10^-10]] // Log10 // N[#, 10] &) //    Evaluate, {u, 0, 3}, PlotRange -> All] 

I get an incomplete plot; the values of the function for u>1.7 (or so) are apparently left unevaluated:

Out[4]=  

How to fix this?