Display shows Err5 and unit does not refill brine tank at the end of regeneration

Safety first: Turn off power and place the softener in bypass. Depressurize the system by opening a faucet.

Step-by-step checks:

• 1. Confirm inlet pressure: Ensure the main water supply and Marlo bypass are fully open. Very low pressure can prevent proper brine refill.
• 2. Inspect refill flow control: Locate the refill flow control (often a small button or orifice in the valve body or brine line). Remove it and check for debris or scale. Clean with water and a soft brush.
• 3. Check refill valve operation: On models with a separate refill valve or solenoid, disconnect the valve and inspect for mechanical sticking or debris. Manually move the plunger if possible to verify free movement.
• 4. Electrical test (if solenoid-equipped): During the brine refill stage, measure voltage at the refill solenoid connector. If the control board is not sending power but the program is correct, the board may be faulty.
• 5. Manual refill test: With the unit in service, slowly open the brine line at the valve to see if water flows into the brine tank. If manual flow is good but automatic refill fails, focus on the control and valve actuation.

When to replace parts: Replace the Marlo refill flow control if it is damaged or permanently restricted. Replace the brine refill valve/solenoid if it does not open under power or is mechanically stuck.