All I have done at this stage is replace the boilers mechanical thermostat by a thermocouple with simple control electronics. This is not a PID just a replacement of the mechanical device with a higher speed electronic control using 1C gap between on/off. Could go down to 0.25C for tighter control but there could be an issue of noise limiting accuracy plus the idea is to PID. Being under program control I can simply adjust temperature.
The graph in the attached file is the before and after fitting an electronic thermostat. Took a shot at about 840 seconds to see what the response of the electronic control would be. The two graphs are offset because I started the electronic control run at a lower temperature and it makes it easier to see what is happening. You can also see the effect of the group head/porta filter coming upto temperature from the changes in the period of the ramps.


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