The L9 error code on a Mitsubishi Electric Ecodan Air Source Heat Pump indicates a low water flow rate in the primary pipework circuit. This could be due to: Water circulation issues, Air in the circuit, and A zone valve or pump that isn't energizing You can try looking for restrictions in the water circuit, such as damaged pipework or valves or flexes that may be kinked. An L9 Error Code can occur on a Mitsubishi Electric Air Source Heat Pump when a Flow Sensor or Flow Swit