The best way to wash nappies is to do a cold wash first, then either a 40 or 60 degree wash with extra rinse afterwards. Use anything from a teaspoon to a half dose of bio washing powder depending on your water hardness (teaspoon for very soft water, half dose for very hard).
I'd do a maintenance wash on your machine (empty machine, 90 degree wash with a full dose of bio powder) then do another strip wash on the nappies. Wash them on cold with a full dose of bio powder. Then do a 60 degree wash with no powder & do 3 or 4 extra rinses afterwards.
My little one has eczema & I just do an extra rinse on her clothes & nappies & it doesn't afffect the eczema.