A new system has no pressure on the gauge but fluid rushes in the lines. What could be the cause?

The scenario presented suggests that despite the gauge displaying no pressure, fluid is moving through the lines. This situation can occur when a pilot valve is not functioning correctly, particularly due to contamination on its seat. When debris or contamination settles on the pilot valve seat, it may prevent the valve from closing properly, leading to fluid flow in the lines while the system gauge remains at zero pressure.

This situation indicates the pilot valve might be inadvertently allowing fluid to pass without generating system pressure, which is often responsible for controlling the system’s operation based on pressure readings. The unimpeded flow of fluid without the pressure buildup can be directly attributed to this malfunction.

Other factors like a closed inlet line or low fluid in the reservoir would typically prevent fluid flow entirely, while a clogged inlet strainer would restrict flow but might still produce some pressure readings, depending on the extent of the blockage. However, in this case, the correct identification of contamination on the seat of the pilot valve aligns directly with the symptoms of the system described.