Bosch Dishwasher error code E12
Limescale in the heat pump
Quick answer
On Bosch Dishwasher (2000s onward), E12 is a fault. It means limescale in the heat pump. A first thing to check: Mineral scale from hard water building on the heat pump or exchanger surfaces.
- Applies to
- Bosch Dishwasher
- Bosch dishwasher codes · Dishwasher · 2000s onward
- Type of code
- Fault
- Urgency: Book a technician
- First safe check
- Use a descaler intended for the appliance and follow its instructions, because acid descalers are not interchangeable across every machine.
What E12 means on this model
Scale has built up in the heat pump chamber until the machine will not heat properly, and it is the one Bosch fault with a clear owner-level answer. Descaling with the product made for the machine restores the heating, and in hard water areas it is a routine job rather than a repair.
Symptoms you will notice
- Code appears during the heating or drying stage of a cycle
- Dishes come out dirty or wetter than they used to from the same load
- Cycle runs noticeably longer than it did a year ago
- Machine heats slowly, or the drying stage does very little
Common causes
The code tells you what the control detected, not which part failed. These are the causes we see most often, roughly in order of likelihood:
- Mineral scale from hard water building on the heat pump or exchanger surfaces
- Descaling never done on a machine in a hard water area
- Residue from detergent or rinse aid left to dry in the chamber
- Air gap in the installation that lets the machine run hotter than its design
What you can safely check
These are homeowner-level checks. None of them need you to open a live electrical compartment or work on gas.
- Use a descaler intended for the appliance and follow its instructions, because acid descalers are not interchangeable across every machine.
- Run the descaling cycle with the machine empty and the filter in place.
- Confirm the supply valve is fully open, since a starved fill makes scaling worse by concentrating every cycle.
- On machines with a water softener, check the salt level and that the softener is actually enabled.
Do not do these
- ×Do not pour vinegar or a household acid into a heat pump, a Zeolite chamber, or a sealed refrigeration circuit.
- ×Do not descale a machine that is still hot, and do not interrupt a descaling cycle partway through.
- ×Do not use a descaler on a machine whose manual does not list descaling, because some manufacturers void the warranty on the heat pump if it is opened.
When to call a technician
Worth scheduling, and worth your own checks first
You can usually keep living with this for a short while, but it will not fix itself. Do the safe checks below first, because a tripped switch or a blocked airflow is a five-minute fix that would otherwise cost you a service call.
- If the appliance has stopped mid-cycle, is making a noise you have not heard before, or smells burnt, stop reading here and call. Those are symptoms of something the fault code does not describe well enough.
Descaling is entirely a homeowner task when the manufacturer lists it. Clearing a heat pump that is already seized open is not.
What it costs to fix
Parts
Appliance descaler $15 to $30. Water softener salt $10 to $25. Nothing else if the fault is genuinely scale.
Labor
An hour for a descaling cycle. A technician visit to clear a heat pump by hand runs $150 to $300.
DIY or technician
Descaling is entirely a homeowner task when the manufacturer lists it. Clearing a heat pump that is already seized open is not.
Typical US part and labor ranges, 2026. They vary by region, model and contractor, so treat them as a planning figure, not a quote.
Scope of this code
- Code table
- Bosch dishwasher codes
- Models in scope
- Bosch Dishwasher, 2005 onward
- Checked
- Confirm on your own unit
- Find the model number on the data plate, then check this code in the service manual for that model. Manufacturers revise code tables between model years, and a revised board can renumber a fault.