Thank you drank for you your answer!! We never would have been able to fix our machine without without it! When our 15 yr old impressa s9 started showing error 4 we bought the jura tool on Amazon ($10) to open the back of the unit. We knew error 4 indicated an issue with temperature readings from the water heating units, either that the temperature reading was too high or erroneous. When I called jura customer service, they wanted $400 plus shipping and handling to fix the machine. So here's the story of how we fixed the machine for $60.
Error 4 is caused by: the thermoblock itself (getting too hot), it's temperature sensor (the unit is heating correctly but the sensor is sending an incorrect reading) or the motherboard is broken (heating and sensing is working but the motherboard is interpreting it incorrectly). The error could also be due to a combination of these things.
Once the unit was open we saw two thermoblocks, one near the bottom of the unit and one at the top. The bottom thermoblock is the initial water boiler while the top thermo block further heats up the water to create steam for the milk frother. Using a thermapen, we turned on the jura and checked the temperature of the thermoblocks on startup. Both thermoblocks were rapidly increasing in temperature (the top one actually reached 500 degrees. You can stop it from heating up by running the steam or unplugging the machine).
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In the impressa s9, the bottom thermoblock is very accessible. This is important as you can't test the resistance of the sensors without removing them from the machine. To remove the bottom sensor we unplugged the machine, unplugged the wire from the motherboard and then ran a screwdriver from the top of the unit down to the screw holding the sensor in place. (We usesd a magnet tipped screw driver because we did not want to drop this screw) The bottom sensor has a red wire attached to a metal loop at the end. This temperature sensor is of type NTC. It works because the metal in the sensor loses resistance in a predictable way as it heats up. Next we used a multimeter to test the resistance of the sensor. As drank specified, it was 12k ohms. This sensor and thermoblock was probably working correctly.
The second sensor was harder to get at. I also read online that this is one of the most common reason why the machine breaks. We had high hopes! Reading online it seemed like you basically needed to undo the entire machine to get at that sensor. With a little luck and ingenuity we were able to loop some floss around the sensor, use tweezers to lift the three pins holding it down and yank it out of the machine. Careful not to break the sensor during this process. (But it does take a fair amount of force). (Note: Before pulling it out, we did need to move the thermal fuse off to the side. This fuse is in a plastic tube that is clipped onto the top thermoblock. I believe it cuts power to the top thermoblock if it gets too hot.)
This sensor had an infinite resistance. We had found at least one point of failure! Next we used dranks idea to mimic a temperature sensor reading at the correct heat by connecting a 330 ohm resistor to the temperature connector (see image). When we turned on the machine the error was gone!!! We then purchased the part here:https://www.jura-parts.com/Jura-S7-S8-S9... ($50) and attached the new sensor. Happy brewing!!
How did you clear the error message?
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Hi, a video how to fix your Jura step by step, good luck... http://fixandparts.wix.com/nicknicoloudis#!jura-coffee-machine/c15gy
SOURCE: how do I fix a 'storing 4' (error 4 in Dutch)
error 4 is the ntc sensor on the top thermoblock
change it and the machine will be fine
to check just measure the resistance of the sensor , it should be 12Kohms with room temperature.... the warmer it gets the less resistance
a other quick way to check it is changing it with a resistor of around 330 ohms
the machine will work properly only it thinks the temperature is good while it may not be warm enough yet
to reset the error press the 2 middle buttons for a few seconds while in standby mode
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