Hard to say what is happening, especially as you didn't give us any information about what the configuration was before and after the change.
My guess is that the new router is enforcing either Wireless Isolation or Wireless Guest Mode. Either of these will prevent CC from seeing another computer on your network. Another possibility is that your device is on one network band and the computer running calibre is on another band, and that the router does not permit information transfer between bands.
Another possibility: if you have entered a fixed IP address into CC's connection setup then that could be the problem. The new router will almost certainly use different addresses. If this is the case then change CC to use the default (no address) and see if anything changes.
You don't say what OS is on the machine running calibre. It could be that you need to change the firewall settings because of the new router.
Please tell us the model of the old router and the new router. Also, please send us debug logs for both CC and calibre as described in our FAQ
How do I get help? because the logs would permit us to eliminate some obvious causes and might point at non-obvious causes.