Health Monitor

One thing that you can do are try to use

tcpdump

to grab the traffic to/from the pool member(s) and see what kind of response you're getting.

Another thing would be to verify with

curl

that you're receiving the right response if you send a request to the server with the same parameters your health monitor is using.

And, you can check out my second answer on this question on how to enable monitor logging. Then you can check the log file to see what kind of request/response you're getting.

Hope this helps.