If your Bosch washing machine stops mid-cycle and the F21, the electronic module has detected that the motor isn't rotating at the expected speed or that the water isn't draining properly. This isn't a single problem: it can be due to up to seven different causes, ranging from a clogged filter (the most common and cheapest to fix) to a damaged power module (the least common and most expensive). In this guide, we'll review, from the most likely to the rarest, how to identify what's wrong with your Bosch washing machine and when it's advisable to call a technician.
First of all: unplug the washing machine before handling any components, and do not proceed beyond the filter if you are not experienced with electricity — some of these checks involve measuring electrical components with a multimeter.
Cause 1: Clogged lint filter
This is the most common cause. Coins, buttons, hairpins, and lint accumulate in the filter and obstruct drainage, which the module interprets as a fault and stops the program, displaying F21. Locate the lower front access panel, place a towel and a container underneath, and unscrew the filter to clean it thoroughly.
Cause 2: Blocked drain pump
If the filter is clean and the water still isn't draining, there may be an object stuck inside the pump, or the pump may be worn out from use. With the washing machine unplugged, access the pump (usually behind the filter panel) and check that the impeller spins freely by hand.
Cause 3: Bent or pinched hoses
Check the drain hose behind the washing machine: if it is squashed against the wall or cabinet, or has a sharp bend, the water will not flow at the necessary rate and the module will throw the error for safety reasons.
Cause 4: Worn carbon brushes
If the motor gradually loses power before reaching the failure point, it is likely that the brushes —parts that normally wear out after several years— are worn out and no longer make good contact with the motor's commutator.
Cause 5: Defective tachometer
The tachometer is the sensor that informs the circuit board of the motor's actual speed. If it gives an incorrect reading, the electronics will think the motor isn't running properly, even if it is, and will stop the program. Checking it requires a multimeter (approximate expected resistance: 500-1,200 Ω) and it's best to leave this task to someone with experience.
Cause 6: Damaged power module (inverter)
This is the least common cause and the most expensive to repair. If you've ruled out everything else, the motor control module itself may be faulty. Before buying this part, it's advisable to have a technician confirm the diagnosis, as it's one of the most expensive parts of the washing machine.
Cause 7: Corroded cables or connectors
Humidity and constant vibration can loosen or corrode motor or pump connectors over time. A visual inspection of the accessible wiring, without disconnecting anything if you're inexperienced, can reveal a loose or corroded connector.
Related spare parts
If you have already identified the faulty part, at Electro Cholo we have replacement parts compatible with most Bosch models:
