Display shows “Error 4”; machine may stop during heating or brewing and not complete the cycle.

Safety first: Disconnect power and allow the machine to cool completely before opening.

Step 1 – Power cycle and cool:

• Unplug the machine for 20–30 minutes to allow any thermal protection to reset.
• Plug back in and test; if the error clears temporarily, overheating is likely.

Step 2 – Descale thoroughly:

• Run a full descaling cycle with Jura descaling tablets to remove scale from the brew thermoblock.
• Repeat if the machine has not been descaled for a long time.

Step 3 – Inspect brew thermoblock (advanced):

• Remove the housing (unplug first).
• Locate the main brew thermoblock; check the NTC sensor and wiring for damage.
• Test the thermal fuse for continuity; replace if open.

Step 4 – Replace components:

• Replace a faulty NTC sensor or thermal fuse with original-spec parts.
• If the thermoblock is heavily scaled internally or the heating element is open, replace the entire brew thermoblock assembly.
• If all hardware checks good, the main control board may be misreading the sensor and should be replaced by a professional.