Op amp sample and adjust own output?
Something along these lines is probably what you want.
RV1 adjusts the proportional gain. A PB of around 3% usually works well and is stable, if the system is well designed. Badly designed systems can still oscillate, but proportional controllers are inherently more stable than PI, and can hold the temperature to within a fraction of 1% in many practical circumstances.
RV2 is &quot;manual reset&quot;. Adjust it so the valve is approximately in the correct position for the setpoint with no error. Alternatively, wait for it to settle then adjust it to eliminate any offset under typical operating conditions.



simulate this circuit &ndash; Schematic created using CircuitLab