pH measurement / pH meters and electrodes

How to fix error code E07 on a H138 miniLab pH meter


Q: When I’m trying to calibrate my H138 miniLab pH meter and I go from the pH 7 buffer to the pH 10 buffer, I get error code E07 showing? What is the problem and how can I resolve it?

H138 pH meter
The ISFET H138 portable pH meter by Hach

A: There are several things that may be causing this error;


Wrong buffer set selected

The meter can be calibrated against 2 buffer sets;

  • pH 4.01, 7.00 and 10.01    or
  • pH 4.01, 6.86 and 9.18

If the meter is set to the wrong buffer set it will cause the error, as it is expecting a different buffer than you are using.

Push and hold the CAL1 button then push the power button to change the buffer set. Push CAL1 again to toggle between the parameters.


Buffer order

The buffers should be applied in the order 7 then 4 then 10.

Applying the buffers in the wrong order may cause the meter to see unexpected readings and give the error.


pH 10 Buffer is out of date

Due to the chemicals used to make pH 10 buffers these do tend to go “off” faster than other buffers.

Try performing a 2 point calibration with the pH 7 and 4 buffers only and then read the pH 10 buffer as if it is an unknown sample – does it read correctly?

You can also try reading a different, fresh batch of pH 10 buffer to compare.


Sensor fault

Alternatively the error may be because the sensor has a fault – try cleaning the sensor with cleaning solution and then try to calibrate again.

If the error persists the sensor may have reached the end of it’s life and need replacing with a new sensor – these are easily replaced with no tools needed.


For more information about the H13 series of pH meters follow the links above or contact us;