Rex C100 pulsing instead of heating

Thread Starter


Joined Oct 3, 2022
Hi all

I have a rex c100 hooked up to a SSR and a slow cooker to make a sous vide machine.
I did an auto tune (3.5 hours) tight out of the box and it went fine. Controller out comes on and stays on, water heated up, a little overshoot, a little under shoot, then it kept the temperature perfectly.
The problem is since then when I start the system from cold it immediately starts pulsing the SSR no matter the temperature differential. For example the water is at 20 degrees C, the setpoint is 65, the output of the controller pulses for 0.5s the is off for 3s. So the water heats a few degrees then never gets any hotter.

I have tried default settings, I've redone the auto tune, nothing seems to help.

Any suggestions would be appreciated.


Joined Oct 17, 2019
Firstly upload a circuit/wiring schematic.
What is the exact model number of the C100 you are using?
How are you measuring the temperature? is it the measured value displayed on the C100 or a separate thermometer?