What this code means, briefly
Read F20 as this: the machine has detected heating when none was expected. Stop using it: heat arriving uncommanded is the one washer fault where the risk is to the load and the machine rather than just the result. You can settle whether this is a one-off or a real fault yourself; naming the failed part is not owner work.
Error codes
Reference| Code | Meaning |
|---|---|
| F20 | These error codes indicate there is unexpected heating in your washing machine. |
What you actually observe
- The code appears on a cold or delicate programme — Uncommanded heat shows up soonest on the programmes that should not heat at all.
- The fault moves when the appliance is knocked or something is set down hard on it — A vibration-sensitive fault is a connection fault, and that is half of what this code covers.
- NEAR MISS — several unrelated functions are out at once — That is upstream of the heating circuit and its switching relay — a supply or a control fault — and it is not this code.
What triggers F20, most likely first
- A switching relay stuck closed — It goes first because it is the mechanism by which heat arrives uncommanded: a relay whose contacts have welded keeps the element live regardless of what the control asks for.
- A temperature sensor reading high — A sensor drifting upward makes the control believe there is heat that is not there, which produces the same code with nothing actually overheating.
What to check first, second, third
- Try one cold programme after a full power cycle — A single controlled test tells you whether the fault is live without running a full hot wash.
- Have the harness to the heating circuit and its switching relay inspected where it flexes — Chafe marks and green pins are found by eye once the panel is off, before a meter is needed.
- Have the heating circuit and its switching relay measured at the control connector — One measurement at the board end tests the part and its wiring together, which is exactly what the code covers.
What an owner can safely do
- Cut power at the breaker for a full minute and restore it — This clears a stored fault. A code that returns on the next cycle is live and needs the panel off.
About 5 min
- Cut power at the breaker for a minute, then run one short cold programme and feel the load at the end — One test only. If the load is warm on a cold programme, switch the machine off and leave it off.
About 45 min
- Use the appliance the same way again and note the exact moment the code lands — The trigger point is the most useful thing you can hand a technician, and it costs one session to get.
About 45 min
- STOP HERE — the heating circuit and its switching relay and its wiring are behind a panel — Everything past this point is work next to live terminals, which is where an owner check ends.
Safety first
Safety
Unplug the machine or switch off its breaker before any panel comes off — a capacitor can hold a charge after the power is off. Close the supply tap before touching a hose, expect standing water when a filter comes out, and never work round the door interlock.
When to call a technician
Call straight away if the appliance behaves unpredictably rather than simply missing one function, or if you can see or smell heat damage at a connector.
Nearby codes on the same appliance
Scope of this reading
What is written here is generalized to the Bosch washing machine line rather than to a single family. Deliberately absent: connector positions, wiring colours, part numbers and the service sequences for your particular build, all of which vary across the line and belong in the manual for your model. If a model-specific page for this code has been published it is linked from the index below, and that page outranks this one for your unit.
Links: - [Bosch washing machine error codes](/blog/bosch-washer-error-codes)
The code index
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
