I have an application where I have a jacketed tank that I am struggling to get the PID instruction working in cascade mode.

The idea was to use cascade control to control the main boiler temp (primary loop) by having it set the appropriate jacket temp (minor loop).

Problem is, I can't seem to get this to tune at all. When I try to utilize the autotune function, nothing happens. The autotune reports that it is running, but no outputs are adjusted and it just sits there.

I attempted to tune it manually as well. I tuned the secondary loop by having everything in manual mode while adjusting the P and I parameters of the minor loop until I got relatively stable results. With the minor loop tuned, I put the major loop back into auto and attempted to tune manually. However, while doing this I had the Bias values of both the major and minor loops quickly max out (freeze bias on) which pegged my outputs on their max values. Even as the PV (of both loops) soared passed their respective setpoints, the bias values remained pegged.

Any idea what I'm doing wrong here? Attached are screen shots of the instruction settings.