i'm trying to scan from my ts3520 to my computer but the canon app just says 'cannot communicate with scanner'.

Diagnosis

The "cannot communicate with scanner" error on the Canon PIXMA TS3520 is almost always a result of a broken WSD (Web Services for Devices) handshake or a missing TWAIN driver. While Windows and macOS often auto-install a basic "Class Driver" that allows you to print, these generic drivers frequently lack the bidirectional communication protocols required for scanning. This creates a scenario where the printer is "Online" for printing, but "Offline" or "Not Found" for scanning. Furthermore, the TS3520 relies on a specific port range to send image data back to the PC. If your network profile is set to "Public" instead of "Private," or if a third-party firewall (like Norton or McAfee) is active, the scanner's data packets are dropped by the computer's security layer before they reach the Canon IJ Scan Utility. You can confirm this by attempting to scan via a USB cable; if it works via USB but fails via Wi-Fi, the issue is strictly network permissions or driver configuration.

How to Fix It

To resolve this, you must bypass the generic Windows drivers and establish a dedicated communication path using the full software suite.

1. Disconnect the printer from your computer and turn the printer off.
2. Open Control Panel > Programs and Features and uninstall every entry labeled "Canon TS3500 series" or "Canon IJ Network Scanner Selector."
3. Restart your computer to clear the system cache.
4. Download the TS3500 series Full Driver & Software Package (avoid the "Lite" or "Basic" versions).
5. Run the installer. When prompted for the connection method, select Wireless LAN Connection.
6. When the installer asks to search for the printer, ensure the printer is turned on and the Wi-Fi icon is flashing. If the installer cannot find it, manually enter the printer's IP address (found by pressing the Information button on the printer panel).
7. Once installed, do not use the generic Windows "Scan" app. Instead, open the Canon IJ Scan Utility from your Start Menu.
8. Click Settings... and ensure the "Product Name" dropdown has the "TS3500 series (Network)" selected rather than the "WSD" version.
9. Run a test scan using the "Auto" button in the IJ Scan Utility.

If That Didn't Work

• Change Network Profile to Private: Go to Settings > Network & Internet > Status > Properties. Change the Network Profile from "Public" to "Private." Public profiles block the inbound ports (specifically UDP 161 and TCP 80/443) that the TS3520 uses to send scan data to the PC.
• Disable Windows Image Acquisition (WIA) Conflict: Press Win+R, type services.msc, and hit Enter. Find "Windows Image Acquisition (WIA)." Right-click it, select Properties, set Startup type to "Automatic," and click Start. If it is already running, right-click and select "Restart."
• Assign a Static IP Address: Access the printer's remote UI by typing the printer's IP address into a web browser. Navigate to Network Settings > IPv4 and change "DHCP" to "Manual." Assign a high IP address (e.g., 192.168.1.200) to prevent the router from changing the printer's address, which frequently breaks the scanner link.
• Firewall Exception: Add an exception to your firewall for cnscan.exe and IJScanUtility.exe. These are the specific executables that handle the handshake between the TS3520 hardware and your operating system.

Heads Up

• Avoid WSD Ports: If you see "WSD" in your printer port settings, change it to a Standard TCP/IP Port. WSD is notorious for dropping connections after the computer wakes from sleep.
• Power Cycle Sequence: If the scanner disappears after a power outage, always reboot the router first, then the printer, and finally the computer. This ensures the IP handshake happens in the correct order.
• Firmware Updates: Use the Canon IJ Scan Utility to check for firmware updates. Canon frequently releases patches for the TS3500 series to improve wireless stability.
• USB Fallback: If you are in a high-interference environment (many 2.4GHz devices), the TS3520's small antenna may struggle. A high-quality USB 2.0 A-to-B cable is the only 100% reliable way to avoid communication errors.