How do I troubleshoot a hunting control valve?

A hunting control valve oscillates around its setpoint without stabilizing, and the root cause is typically one of: oversized valve (Cv too large, causing the valve to operate in the bottom 10–20% of its stroke where the gain is highest), incorrect PID tuning (too much integral or proportional gain), sensor placement that introduces dead time (e.g., a strap-on pipe sensor with poor thermal contact), or an unstable differential pressure across the valve. Start by checking the valve authority — if it's below 0.25, the valve is almost certainly oversized; check whether the valve ever exceeds 50% open at design conditions. Next, put the controller in manual and step the valve open by 5–10% increments while observing the coil temperature response to determine the process time constant, then retune the PID loop with an integral time of at least 4× the process time constant. If the problem persists and system pressure is fluctuating, install a PICV or pressure-independent valve to decouple the coil from system pressure variations.