E5 error and the display is frozen or unresponsive

Safety first: Unplug the softener from mains power before opening the control panel. Do not work on live electronics.

• Power reset: Disconnect power for at least 5 minutes to allow capacitors to discharge. Plug back in and observe if the display boots normally or still shows E5.
• Inspect connections: Remove the front cover of the Nobel control head. Check the ribbon cable between the display/keypad and the main PCB. Reseat the connector by unplugging and firmly plugging it back in.
• Check for moisture: Look for condensation, corrosion, or water marks on the board. If moisture is present, dry the area gently with a hair dryer on low heat (from a safe distance) and improve the unit's environmental protection (e.g., fix leaks above, improve ventilation).
• Verify power supply: Use a multimeter (if qualified) to confirm the transformer or power adapter is providing the correct voltage to the control board as specified on the label. Replace the power supply if voltage is out of range.
• Reprogram settings: If the board boots but shows E5 intermittently, enter the installer menu (refer to your Nobel manual) and verify hardness, capacity, and time settings. Save and exit to force a memory write.

If E5 persists after these steps, the main control board is likely defective and should be replaced with the correct Nobel replacement module.