Bunn coffee maker displays E04 and stops mid-brew or will not start brewing at all.

Safety: Unplug the brewer and shut off the water supply (for plumbed-in models) before servicing the fill system.

Steps:

• 1. Check water supply: Confirm the water shutoff valve is fully open. Inspect the supply line for kinks. Verify adequate water pressure (typically 20–90 psi for Bunn commercial brewers).
• 2. Clean inlet screen: At the water inlet fitting or solenoid valve, remove and clean the small mesh screen. Mineral debris can restrict flow and trigger E04.
• 3. Inspect water level probe: Many Bunn models use a stainless steel level probe in the tank. Remove the probe and clean mineral scale with white vinegar or a descaling solution and a non-abrasive pad. Rinse thoroughly and reinstall.
• 4. Test fill solenoid: With the unit unplugged, check the resistance of the fill solenoid coil. A typical reading is 200–1000 Ω depending on model. An open coil indicates a failed solenoid valve that must be replaced.
• 5. Check wiring and connectors: Ensure the level sensor and solenoid connectors are fully seated on the control board and not corroded.
• 6. Descale tank: If heavy scale is present, perform a full descale of the internal tank following Bunn's instructions. Scale can insulate the probe and cause false level readings.

Note: After cleaning or replacing components, restore water, plug in, and allow the tank to refill and heat. The E04 code should clear once normal fill is detected.