Rinnai Replacement HDC1500i/e Servo Kit (P1500-KITC) The servo assembly on a Rinnai HDC1500i or HDC1500e takes signals from the electronic control board and translates them into precise movement of the internal valves, fine-tuning water flow and gas delivery to keep combustion stable and hot water output consistent. When it's working correctly, you don't notice it — it's when it starts to wear that the effects show up. A worn or faulty servo typically shows itself as inconsistent hot water temperature, reduced output, or flow and valve control fault codes appearing on the display. This genuine Rinnai servo kit is made to the original specification for the HDC1500i/e, restoring the precise valve control the appliance was designed around. ⚠ Important: Installation and servicing must be carried out by a qualified technician