Bosch Dishwasher E21 Error Code — What It Means & How to Fix It

What Does This Error Mean?

E21 on a Bosch dishwasher means the drain pump motor is running but not pumping at the expected speed or rate. The dishwasher can tell when the pump is running but struggling — either because it is partially blocked or the motor is weakening. You may notice the machine draining very slowly, not draining completely, or stopping mid-drain cycle. This is different from E20 (complete drain failure) — E21 means partial drain pump function with degraded performance.

Affected Models

Bosch Serie 4 SMV46
Bosch Serie 6 SMS68
Bosch Serie 8 SMV88
Bosch Silence Plus SMV50
Most Bosch dishwashers 2015 and newer

Common Causes

Partial blockage in the drain pump impeller slowing it down without stopping it completely
Filter clogged and restricting flow to the drain pump, causing it to work harder
Worn drain pump motor bearings causing reduced pump speed
Drain hose kinked or partially blocked, increasing back pressure on the pump
Small debris caught in the pump impeller causing intermittent restriction

How to Fix It

Clean the dishwasher filter and sump area thoroughly. A partially blocked filter is the most common cause of E21 — it makes the pump struggle to move water.

Remove the filter, rinse under the tap, and use a soft brush to clear food debris and grease from all mesh surfaces.
Inspect the drain hose for partial kinks or restrictions. Even a slight bend in the drain hose increases back-pressure and can cause the pump to slow below expected speed.

Check the full length of the drain hose from the machine to where it connects under the sink.
Check the sink drain and garbage disposal connection for partial blockages. Grease buildup in the sink drain can create back-pressure that slows dishwasher drainage.

Pour boiling water mixed with dish soap down the sink drain to clear minor grease buildup.
After cleaning the filter and hose, reset the dishwasher and run a short cycle. If E21 does not return, the cleaning resolved the restriction.

Press and hold the On/Off button for 3 seconds to reset before starting a new cycle.
If E21 returns after cleaning, the drain pump impeller or motor needs professional inspection. Have a Bosch technician access the pump, check for debris, and test motor speed.

A failing drain pump motor is usually replaced rather than repaired — expect £50 to £100 / $60 to $120 for the part.

When to Call a Professional

If cleaning the filter and checking the drain hose does not clear E21, the drain pump may have debris in the impeller or a failing motor. Accessing the pump impeller requires removing the lower part of the dishwasher. A Bosch-certified technician can quickly determine whether a cleaning or a full pump replacement is needed.

Frequently Asked Questions

What is the difference between E20 and E21 on a Bosch dishwasher?

E20 means the drain pump has failed to drain at all — no water movement detected. E21 means the pump is running but below expected speed — partial drainage only. E21 is often easier to fix because the pump is still working, just restricted or partially blocked.

Can E21 cause water to back up into my sink?

If the drain hose connects to a sink drain that is also partially blocked, slow dishwasher drainage can cause water to back up. Fix the sink drain blockage and the dishwasher drain issue together to prevent this. A gurgling sound from the sink during the dishwasher drain cycle is a sign the sink drain needs attention.

Is E21 a sign my Bosch dishwasher needs replacing?

Not necessarily. E21 is usually a repair rather than a replacement situation. A blocked pump impeller or a failing pump motor are fixable components. Bosch dishwashers are built to last 10 to 15 years — a pump repair partway through that lifespan is generally worth the cost.