flooding - renters insurance wont cover - is landlord responsible

my apartment flooded. my renters insurance wont cover because of broken sump pump is landlord responsible

Depends.
Did the LL break the sump pump?
Did you inform the LL in writing previously that the pump was broken?
Can you prove that the LL had knowledge that the pump would fail or could fail and flood the place?

If you can answer yes to any of these, he's responsible. If the answers are all no, there isn't any way to make him responsible. He's obligated to fix it now that he knows it's broke, but without prior knowledge, neither of you could have forseen this problem.