André wrote:

I’m building the same setup but I’ll modifying this part. I’ll be adding an extra selector to control which PID controls the element in the HLT.

The Mash PID should be controlling the element in the HLT during recirculation phases of mashing. The temperature that really matters is the liquid in the Mash tank. You don’t really need to know what water temperature will get you correct mash temperature. The Mash PID will activate the element in HLT to get to your mashing SP temperature. You’d get the same result by manually increasing SP in HLT and checking if Mash temperature is ok but not beneficiating from PID controller on your Mash tank.

I know what you mean and this has been discussed a lot. I agree with this discussion and I would not use the sensor at the output of the mash tun to control the element. There is too much lag time between the heat source and the sensor. Just try it, but I don’t think that I’ll work that good.