"Probeer niet om zelf de verwarming te repareren."
Translation:Do not try to repair the heating yourself.
A bit puzzled why my answer...do not try to repair the heating system yourself...was rejected, and proposed with...do not try to repair the heating by yourself..given the above correct answer?
Probably because there's no word for "system" in the original Dutch sentence. Whenever your answer is rejected. Duolingo automatically provides an alternative answer, which may or may not make sense. It happens in other language courses as well, at least in Spanish.