Garbage disposal runs but water backs up into sink; grinding seems normal but sink drains very slowly or not at all, internal LED flashes four times when unit is running.

Safety first: Turn off the disposal switch and circuit breaker. Do not work under the sink with power on.

• Check for standing water: If the sink is full, bail out excess water into a bucket to reduce spillage when disconnecting pipes.
• Remove the P-trap: Place a pan under the trap. Loosen the slip nuts on the P-trap and remove it. Clear any food sludge or obstructions and rinse thoroughly.
• Inspect the disposal discharge: With the trap removed, look into the Reginox discharge outlet and elbow. Use a small brush or flexible bottle brush to clear buildup.
• Verify dishwasher knockout: If a dishwasher is connected, ensure the internal knockout plug in the disposal’s dishwasher inlet was fully removed during installation. If partially intact, carefully break and remove remaining plastic with pliers (with unit disconnected from power).
• Reassemble and test: Reinstall the P-trap and tighten slip nuts. Restore power, run cold water, and briefly operate the disposal. Check for proper drainage and leaks at all joints.