Bosch Washer E20 Error — Unexpected Heating Fix

What it means

Bosch washer E20 error (also F20) means unexpected heating has been detected — Bosch's specific 'Unexpected heating' code.
The heater is being driven on when the control board didn't request it, or the temperature sensor is reporting a heat spike.
The washer cuts power to the heater to prevent damage.

Affected Models

Bosch Serie 2 / Serie 4 / Serie 6 / Serie 8 washing machines
Bosch Logixx, Maxx, Classixx ranges (older naming)
Bosch WAW, WAT, WAY, WAQ model series
Bosch Varioperfect washers
Same codes appear on Siemens and Neff washers (shared platform)

Common Causes

Heater relay on control board stuck closed
Control board fault driving the heater incorrectly
Temperature sensor (thermistor) faulty — false readings
Wiring short between heater and control board
Recent power surge damaged the heater control circuit

How to Fix It

Power-cycle the washer.

Unplug for 60 seconds, plug back in.
If E20 was a one-off relay glitch, a clean reboot may clear it.
If E20 returns immediately, stop using the washer and arrange repair.
Don't keep restarting.

Repeated restarts through E20 risk overheating the wash water (potentially scalding) and damaging clothes.
The protection is there for a reason; don't bypass it.
Run a cold wash to check.

If you must use the washer in the meantime, try a cold-only cycle.
Cold doesn't use the heater and avoids the failed circuit.
If E20 still appears even on cold, the sensor is at fault, not just the heater.
Call a technician.

E20 needs a technician with a multimeter to diagnose whether the issue is the heater, the relay, the sensor, or the control board.
Repair cost varies from £80 (sensor) to £250+ (control board).

When to Call a Professional

E20 is a serious fault — the washer is protecting itself from a heater that won't turn off.
Don't ignore E20 or repeatedly restart through it; arrange technician inspection.
Control board or heater replacement is usually needed.

Frequently Asked Questions

Is Bosch E20 dangerous?

It can be — but the washer's protection cut-out reduces the risk significantly.
The underlying fault is that the heater could be driven on when it shouldn't be, which would scald wash water and potentially damage clothes or the drum.
Bosch designed E20 specifically to detect this and shut off heater power immediately.
You're safe as long as you stop using the washer once E20 appears; the danger comes from forcing the washer to run through repeated E20 errors and bypassing the protection.