Host Check Timed Out + passive checks



I have setup a distributed monitoring.

several clients of ours are sending service check results to our central management server.

This works fine for the service checks, but for almost all my hosts I have the error : host check timed out, host check scheduled

some host states are up, down, unreachable, pending…

Note: host checks are not send from the distributed servers.

what could be wrong here?

I thought that in passive mode the hosts are put in up/ down mode according to the services

thank you in advance