Bosch Washing Machine: Intermittent Washing and Water Filling - Maintenance Theory
For electromechanical fully automatic washing machines, the programmer contacts connected during water filling and washing states are identical. The difference lies in the open or closed state of the water level switch contacts. During water filling, the normally closed contact of the water level switch is connected; during washing, the normally open contact of the water level switch is connected. For microprocessor-controlled fully automatic washing machines, the microprocessor determines the open or closed state based on the received potential of the water level switch contact. During washing, if the microprocessor receives a signal indicating that the normally open contact has opened (or the normally closed contact has closed), it will disconnect the washing circuit and connect the water filling circuit, switching from washing to water filling. Therefore, when the washing machine exhibits intermittent washing and water filling issues, it indicates a change in the open or closed state of the water level switch contacts.
There are two main causes:
1. Leakage in the washing machine. A leaking washing machine will lower the water level. When the water level drops to a certain extent, the water level switch contacts switch over, causing the circuit to transition from the washing circuit to the water filling circuit. When the water level rises again, the water level switch contacts switch back to reconnect the washing circuit. In this fault scenario, the water level in the wash tub (inner tub) fluctuates between rising and falling. Resolving the leakage issue will restore normal operation of the washing machine.
2. Air leaks in the tubing or rubber diaphragm of the water level switch. Air leaks reduce the pressure in the water level switch chamber. When the pressure decreases to a certain point, the water level switch contacts switch over. After water filling, the pressure in the water level switch chamber increases again, causing another contact switch-over. This cycle repeats, leading to intermittent washing and water filling faults, with the water level in the wash tub continuously rising. The solution involves identifying the air leak in the water level switch, repairing the leak, or replacing the water level switch.
Source: http://blog.sina.com.cn/boshixiyji