Water backs up into the machine from the drain or sink when not running.

Safety first: Turn off power and avoid contact with contaminated water. Follow local plumbing codes.

Step-by-step checks:

• Verify drain hose routing: Ensure the drain hose rises to the proper standpipe height before going to the drain, as specified by CMA.
• Check air gap: If an air gap is installed, confirm it is not blocked and is above the flood level of the sink.
• Inspect floor drain: Make sure the floor drain is not clogged or backing up. Have a plumber clear building drains if necessary.
• Correct plumbing connections: The dishmachine drain should not be hard-piped directly into a sewer line without proper air gap or trap per code.

When to call a technician: Persistent backflow issues may require both a plumber and a CMA technician to correct installation.