Display shows E4 and brewing stops; sometimes accompanied by water leaking inside the machine.

Safety first: Unplug the unit and allow it to cool. Water and electricity are a dangerous combination.

• Check water tank and filter: Remove the Tristar water reservoir, clean the outlet valve at the bottom, and ensure any removable inlet filter screen is not clogged.
• Prime the pump: Fill the tank completely, reseat it, then start a brew cycle without coffee. If the pump is noisy but no water flows, stop the cycle, wait 30 seconds, and try again several times to clear an air lock.
• Descale: Mineral buildup can block the flow meter or pump. Run a descaling cycle with descaler or vinegar solution, then flush with clean water.
• Internal inspection (advanced): Remove the back or bottom cover to access the vibration pump and inline flow meter (usually a small plastic disc with two hoses and a wire harness). Check hoses for kinks, leaks, or blockages. Ensure the flow meter connector is firmly attached to the control PCB.

Note: If the pump is silent during a brew command, the pump or control board may be defective. Replacement is recommended via a technician.