What E:20 Means
The heat pump is the combined circulation pump and heater that drives water through the spray arms, and E:20 is logged when its motor windings do not measure correctly. Bosch's action is to take a resistance reading across any two of the three motor terminals and compare it with the figure published for that pump; a correct reading points at the power module instead, a wrong one at the pump. The chart also flags this code when the heat pump harness is disconnected or damaged.
Common Causes of E:20
- Heat pump motor winding open or shorted
- Heat pump harness disconnected or damaged
- Power module unable to drive the pump correctly
🔧 One Safe Check You Can Try
There is no safe home test here. If the machine is silent where you would normally hear the wash pump spinning up, that is worth reporting, but the diagnosis itself is a meter reading on a dead machine.
⚠ Why You Shouldn't Go Further Than That
- Bosch's own chart notes that a dishwasher will refuse to run at all if it detects a disconnected pump, which is a safety check rather than an inconvenience.
- The resistance figure that decides between pump and module is pump-specific, so a reading taken without it proves nothing either way.
- Replacing the heat pump means breaking into the water circuit under the tub and re-sealing it, with the machine out of its housing.
- This is one of the more expensive parts in the machine, and buying it on a guess when the harness was at fault is a costly mistake.
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.