Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.

Do you know what the time is that the exception occurs and are you able to determine what else is happening at that time? Do you know what specific line of code is getting the exception so you know what is being attempted? Yes, I understand it is not just one place, but it still helps to know what the specific line of code is for each occurance.
 
I am not familiar with SQL Server enough to help you with the following, but perhaps you can add code to determine if the dataabase is available and if it is then lock it so other maintenance will wait. I am sorry that I can't help with that though.
 
You could add code to your exception processing so that the service can wait a while and then try again.

That am saying there might a Timeout reset happening.
check your timeout value and try increasing.
 

It seems a DB problem, but i connected through Sql Management studio and iam able to do everything through it (Like querying,updating etc...), just through code is the problem.
The service is calling DB very frequently. Since three hours the service is responding well and no sign of DB overloads. Also it had been on for 20 days without rest and everything was well.
I will post the message if i get this exception again, i already cleared my logs before.
The additional insight into the problem is every method going to DB suffers the same exception. Like simple update statement running within a second now takes more than 30 seconds when this problem comes up.
So i got curious as whats the main issue.
Hope this helps to get hold of problem.
 

1. Connection Timeout in connectionstring
2. SQLCommand Connection Timeout.