Bosch E12 fault codewhat it means and how to fix it
The heating element has furred up with limescale. Descaling fixes today; setting the water softener correctly stops it coming back.
Take care
What E12 means
Bosch give E12 as the heating element being furred up, and on machines that show the long-form code E:20-60 their GB manual words it as the appliance having detected a calcified heating element; Siemens’ website has it as the heating element being calcified or soiled. The official remedy is two steps: descale the appliance, and operate it with the water softening system. That second step is the one that matters, because descaling without addressing the cause simply resets the clock.
Every Bosch dishwasher has a built-in water softener with a salt reservoir, and it has a hardness setting that has to match your local water. The factory default is H04, which covers 16 to 20 degrees Clark. A great deal of southern and eastern England is harder than that, which means a large number of UK machines are running under-softened straight out of the box and quietly scaling up their own heating element.
Bosch state the threshold plainly: water with a hardness above 9 degrees Clark must be softened to avoid damage to the appliance. On older machines with no numeric display this code shows as the salt refill indicator flashing, which owners reliably read as "needs salt" — they top it up, the light keeps flashing, and they conclude the machine is broken. A flashing salt light and a steady one are different messages.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Water softener set too soft for your area | The factory default of H04 covers 16 to 20 degrees Clark. Much of England is harder, so the default is wrong for a lot of UK homes. | Common |
| Salt reservoir empty or never filled | The softener cannot work without salt. Plenty of machines have never had any, particularly where the owner uses all-in-one tablets and assumed that covered it. | Common |
| Salt tablets used instead of dishwasher salt | Siemens document this specifically: the sensor does not detect salt tablets. The reservoir looks full and the machine believes it is empty. | Occasional |
| Salt sensor dirty | Bosch note that a dirty sensor makes the machine assume salt is present when it is not. Worth mentioning if the salt light behaves oddly. | Occasional |
What to try yourself
Find your water hardness. Your water company publishes it for your postcode, and Bosch express the setting in degrees Clark, which is the unit UK suppliers use.
Check the machine’s hardness setting and correct it. Bosch’s scale runs H00 for very soft up to H07 for 39 to 62 degrees Clark, with H05 covering 21 to 26 and H06 covering 27 to 38. The factory setting is H04, so if you are in a hard water area it almost certainly needs raising.
Fill the salt reservoir with dishwasher salt. Bosch are specific: only special salt for dishwashers, not salt tablets and not table salt. Bosch UK add that table salt, sea salt and kosher salt can actually increase water hardness and damage the appliance.
Start a programme immediately after filling. Bosch warn that salt spilled in the tub causes corrosion, and running a cycle straight away washes it out.Descale the machine using a proprietary dishwasher descaler, following the product instructions with the machine empty.
Do not use industrial or strongly caustic cleaners, and do not put aluminium items such as extractor hood grease filters through with them. Bosch warn that combination can cause an explosion.Expect cycles to take slightly longer afterwards. Bosch note that the softener regenerates before the end of the main rinse and that this increases run time — that is normal, not a new fault.
Get a qualified appliance engineer to look at your Bosch E12
We do not pass enquiries to a repair firm, so there is no form here. When you book a qualified appliance engineer, tell them the make, the model and the exact code or message on the display, and ask whether they carry parts for this make — that is what turns one visit into a repair rather than a quote.
What it costs to fix
Typical repair cost
£0–£240
Time on site
45 minutes
A descaler and a box of salt is under £15 and resolves most cases. If the element has already failed, a replacement is typically £140 to £240 fitted, and on many Bosch machines it is integrated with the pump housing which pushes the cost up.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
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Related Bosch fault codes
- E15Stop — call an engineerThe water protection system has activated — there is water in the base of the machine. Turn the tap off and call service. Do not tilt it, whatever else you read.Related: same brand
- E24Get it checkedThe machine cannot drain. Bosch publish a full owner procedure for this one, and two warnings about doing it that their UK page leaves out.Related: same brand
- E18Get it checkedWater is not getting in. Bosch publish a full owner procedure including a flow rate you can measure with a jug.Related: same brand
- E22Get it checkedThe filters are soiled or blocked. Bosch give a one-line remedy — clean them — and it is genuinely the whole job.Related: same brand
- E16Stop — call an engineerWater is running into the machine continuously, whether or not it is switched on. Bosch give the same instruction as for a leak: tap off, call service.Related: same brand
- E27Get it checkedThe mains voltage is too low. Bosch state plainly that this is not a fault on the appliance — you want an electrician, not an appliance engineer.Related: same brand
Own a Bosch dishwasher? Save it and its codes come first next time.
Related guides
Common questions about Bosch E12
I use all-in-one tablets. Do I still need salt?
Above 26 degrees Clark, yes. Bosch say combined detergents with salt replacement substances generally only work up to 26 degrees Clark without adding special salt, and that the softener should only be switched off below that or where the water is genuinely soft at 0 to 8 degrees.
Why does the salt light stay on after I have filled it?
Most likely you have used salt tablets. Siemens document this exactly: the sensor does not detect salt tablets, and their remedy is to use a different salt rather than to book a repair. Bosch separately note a dirty salt sensor can cause the machine to misread the level.
Can I use ordinary table salt?
No. Bosch’s manual says only special dishwasher salt, not salt tablets and not table salt. Bosch UK go further and warn that table salt, sea salt and kosher salt can increase water hardness and lead to appliance damage. It is a few pounds a box and it protects a component that costs a great deal more.
My machine has no display and the salt light is flashing.
On those machines a flashing salt indicator is this code — a calcified heating element — rather than a request for salt. A steady light means top it up. It is an easy and very common thing to misread.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
- Manufacturer support portal
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.