Dishwasher
E12
The E12 error code on a Bosch dishwasher indicates a limescale build-up on the heating element or a fault with the heater circuit — it’s a moderately serious fault that will stop your machine from heating water properly but is often fixable without a professional.
What does this error mean?
Bosch uses E12 to flag that the flow heater (the component that heats water during a cycle) has become heavily scaled or is not reaching the correct temperature within the expected time. The dishwasher’s internal sensors detect that the water isn’t heating efficiently and shut the cycle down as a precaution. In hard-water areas of the UK — particularly London, the South East, and the Midlands — this is one of the most common Bosch dishwasher faults.
Est. repair cost
£80–£150 professional repair (parts + labour); £0–£15 DIY descaling products if caught early
🔍 Likely causes
🛠️ Step-by-step fix
Run a hot descaling cycle: add a dishwasher descaler (e.g. Finish Dishwasher Cleaner or Durgol) to the empty machine and run the hottest programme available (typically 70°C). This alone clears E12 in many cases.
Check and refill the salt reservoir: open the cap on the dishwasher floor, top up with dishwasher salt (not table salt), and reset the salt indicator. Ensure the water softener setting in the programme menu matches your local water hardness.
Clean the filters and spray arms: remove the bottom basket, unscrew the cylindrical filter, and rinse it under the tap. Clear any blocked spray arm holes with a toothpick. Restricted water flow can contribute to heater faults.
Reset the machine: switch the dishwasher off at the mains, wait 60 seconds, then switch it back on. Attempt a new cycle — a temporary sensor glitch can trigger E12 and a hard reset may clear it.
Inspect the inlet hose and water supply valve: pull the machine forward slightly and check that the hose behind it is not kinked or trapped. Ensure the isolator valve under the sink is fully open.
If the error persists after all the above, stop — the heater element, NTC sensor, or control board likely needs replacing. These parts sit inside the appliance base and require a qualified engineer to access and test safely.
📞 When to call a professional
Call an appliance engineer if the E12 code returns after descaling, refilling salt, and resetting the machine. Tell them you have a Bosch dishwasher showing E12 and that you have already descaled it — this helps them arrive prepared with an NTC sensor or flow heater element. Replacing internal heating components involves accessing live electrical parts inside the appliance and must not be attempted as a DIY job.
⚖️ Repair or replace?
A professional repair for E12 — typically a new flow heater or NTC sensor — costs between £100 and £180 including labour and parts in the UK. If your Bosch dishwasher is under 7 years old, repair is almost always the right call given that a comparable new machine costs £400–£700. If it’s over 10 years old and this isn’t the first fault, replacement is worth serious consideration.