Ruud tankless water heater shows error code 65; unit may not respond correctly to recirculation or remote commands.

Safety first: Turn OFF power before working on wiring.

• Step 1 – Check remote cable: Inspect the cable between the Ruud heater and remote controller for cuts, staples through the wire, or loose connections. Ensure polarity (+/–) is correct at both ends.
• Step 2 – Reseat connectors: Disconnect and reconnect the remote cable at the control board and remote.
• Step 3 – Test with short cable: Temporarily connect the remote using a short known-good cable near the unit. If error 65 clears, replace the original cable run.
• Step 4 – Replace remote controller: If wiring is good but the error persists, replace the OEM Ruud remote controller.

If communication issues remain, the main control board may be defective and should be serviced by a professional.