E12
Bosch Dishwasher
Severity: ModerateWhat Does This Error Mean?
E12 on a Bosch dishwasher means there is a significant limescale buildup on the heating element. Over time, hard water minerals deposit a thick layer of scale on the heater, reducing its efficiency and eventually causing it to overheat or fail. Your dishwasher may take longer to reach temperature, dishes may not dry well, or the machine may stop mid-cycle. Descaling the dishwasher usually resolves this error.
Affected Models
- Bosch Serie 2 SMS25
- Bosch Serie 4 SMV46
- Bosch Serie 6 SMS68
- Bosch Serie 8 SMV88
- Most Bosch built-in and freestanding dishwashers
Common Causes
- Heavy limescale buildup on the heating element from hard water over months or years
- Dishwasher salt reservoir is empty or the salt dispenser is blocked
- Water softener system inside the dishwasher is not functioning correctly
- Hard water in the area without a water softener installed in the home
- Heating element is damaged or failing due to scale-related overheating
How to Fix It
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Check the dishwasher salt level. Open the salt cap (usually on the floor of the tub) and fill it with dishwasher-specific regeneration salt if it is low. Dishwasher salt is NOT table salt.
Running without salt in a hard water area causes rapid scale buildup. The salt regenerates the dishwasher's internal ion exchange softener.
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Run a full descaling cycle. Place a dishwasher descaler product (such as Bosch Descaler or a citric acid-based tablet) in the detergent drawer and run the hottest cycle available with an empty machine.
Use a descaler specifically designed for dishwashers — white vinegar can damage rubber seals over time.
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After the descaling cycle, check inside the tub for white deposits. Run another empty hot cycle with descaler if significant deposits remain visible on the heating element at the bottom.
Heavy scale buildup may require two or three descaling cycles to fully clear.
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Check and set the water hardness level in the dishwasher settings. Consult your manual for how to access the water hardness setting. Setting it correctly ensures the salt regeneration cycle runs at the right frequency.
Your local water company can tell you the hardness level of your water supply — usually measured in degrees (°dH or °fH).
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If E12 returns after descaling and refilling salt, have a Bosch technician test the heating element and the water softener regeneration valve. Either component may need replacement.
Bosch heating elements typically cost £50 to £120 / $60 to $150 for the part.
When to Call a Professional
If descaling does not resolve E12, the heating element may be physically damaged and need replacement. A Bosch-certified technician can test the heating element and water softener system. In very hard water areas, professional descaling and softener service may be more effective than DIY descaler products.
Frequently Asked Questions
How do I prevent E12 from recurring?
Keep the dishwasher salt reservoir topped up at all times. Set the water hardness correctly in the settings. Run a monthly descaling cycle as preventive maintenance. In very hard water areas, consider installing a whole-house water softener.
Can I use vinegar instead of dishwasher descaler for E12?
Vinegar can dissolve limescale but it can also degrade rubber door seals and gaskets over time with repeated use. A proper citric acid-based dishwasher descaler is safer and more effective. Bosch sells its own branded descaler tablets, or you can use any dishwasher-compatible descaler product.
How often should I use dishwasher salt?
Fill the salt reservoir whenever the salt indicator light comes on — typically every 4 to 8 weeks depending on water hardness and how often you use the machine. In very hard water areas (above 21°dH), you may need to refill it every 2 to 3 weeks.