HTTP Error 503. The service is unavailable

Hello

I regularly undergo an HTTP Error 503 error when I browse my web site (shared environment)

 Whe I ask my ISP about this issue, I get the following message:

Hello, Please note each customer's account runs in their own application pool. We have limited the amount of server resources an application can utilize before being recycled, here is the criteria: Windows Server 2008/IIS 7 32 bit :

* Idle timeout set to 20 minutes. (Information is NOT logged) *

 Memory threshold set to 200 MB.

* CPU limit set to 70% utilization over 300 seconds (5 minutes). It looks like your site is meeting the Idle timeout criteria.

How could I have a clue about what is responsible of such a situation ?

Thanks Jacques