There is a leak in the Water Circuit. Replace O-Rings and hoses as necessary.
Replace Membrane Regulator (Most Common). Often times, the water pump will become increasingly noisy due to a blockage inside the Membrane Regulator, which in turn, prevents the required pressure to maintain a uniform flow of water throughout the machine from passing through the regulator.
Indicates a blockage in the Water Circuit, preventing the free flow of water. Replace blocked components (valves/connectors/tubes/hoses) as necessary.
The Flow meter may need to be cleaned or replaced. Open the top of the Flow-Meter by turning the top counter-clockwise to clean the inside.
The Solenoid Valve may be clogged with scale. If the Solenoid Valve connects the pressure hoses via a Legris Connector (Push Connect), then these can be removed and cleaned or replaced.
If the Solenoid Valve connects the pressure hoses via a Hair Pin Clip connection, then the entire valve needs to be replaced.