What 1 Means
On older Bosch dishwashers with a two-digit display, running the service test programme produces a number that reports what failed. A value of 1 is the Aqua Sensor fault, Bosch's optical turbidity sensor also branded Sensotronic on that generation. The manual notes that these numbers add together when more than one fault is present, so a displayed 3 means this fault plus the heating fault.
Common Causes of 1
- Grease or scale film over the Aqua Sensor window
- Sensor failed or its harness damaged
- Sensor missing after previous work on the machine
🔧 One Safe Check You Can Try
Clean the sump thoroughly with the filters removed, since the sensor window sits there and a greasy film over it is the everyday cause. Follow it with an empty hot programme and a proprietary machine cleaner before concluding the part itself has died.
⚠ Why You Shouldn't Go Further Than That
- These machines are now fifteen to twenty years old, and the sensor harness has spent that long in a warm, damp cabinet.
- The sensor window is flush with the sump wall and scratches easily, after which it reads permanently dirty.
- Because the codes add up, a single displayed number can represent two faults, and treating it as one leaves the other in place.
- Reaching the sensor means working under the tub next to the pump wiring on a machine fixed to the cabinetry.
Opening a panel to inspect or repair something yourself doesn't automatically cancel your manufacturer's warranty — but it can risk accidental damage, and some manufacturers do have specific service conditions. Check your product's warranty terms, or ask us, before deciding.