E13 error and the unit reports excessive water usage or regenerates too frequently

Safety first: No internal electrical work is required for basic checks. Do not open the control housing while powered if unqualified.

• Check for leaks: Turn off all taps and water‑using appliances in the house. Observe the Nobel display—if it still shows flow or usage increasing, there is likely a leak. Inspect toilets, outdoor taps, and under‑sink connections.
• Isolate sections: If possible, close branch valves to isolate parts of the plumbing until the flow reading drops to zero. This helps locate the leak.
• Inspect flow meter wiring: If no leak is found but the display shows flow, check the flow meter cable for damage or water ingress. Reseat the connector on the control board.
• Reset usage: After fixing any leaks, clear the error by power‑cycling the unit or using the reset function. Monitor usage over the next 24–48 hours.

If E13 recurs without any actual water flow, the flow meter or control board may be faulty and should be replaced.