Manifold Pressure
Manifold pressure is required to meet manufacturer specifications, which varies by equipment model. Precise setting of the manifold pressure results in clean and efficient flame production at the burner tubes. Efficient flame production saves money, but a clean flame plays a much more important role. Burners operating with a dirty flame will quickly build up soot, which can create blockages in the internal heating passages of the equipment that are difficult to remedy, and can even become dangerous.
The need for manifold pressure adjustments is not unusual, especially on older boilers. When manifold pressure adjustments cannot be achieved, it usually indicates a failed or failing gas valve.