Check the fault p0128 test procedure and possible causes attached below in figure 1, also other than thermostat, temperature sensor is a possible cause. also check the figure 2 how to test it by using hot water and ohmmeter.
the thermostat at the outlet is called control valve check figure 3 you can check and inspect it by using hot water and check if its opening, check figure 5,6 procedure how to remove and reinstall. also test procedure attached below figure 7, 8 for control valve opening temperature is 95 degrees.
check our link below how to check thermostat.
Hope these helps, let us know if you need more help.
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Friday, February 5th, 2021 AT 8:52 AM