Why might a boiler not require a feed pump?

A boiler may not require a feed pump if the operating pressure is below city water pressure because, in this situation, the natural pressure of the city water can be sufficient to overcome the pressure in the boiler. When the boiler operates at a lower pressure than the water supply, the force of gravity and the incoming city water's pressure are adequate to feed water into the boiler. This scenario allows for efficient water supply without the need for an additional mechanical pump to elevate the pressure.

In contrast, when the operating pressure exceeds the city water pressure, a feed pump becomes essential to ensure that water is supplied at the necessary pressure for the boiler's operation. Similarly, high-capacity models may typically require pumps to handle large volumes of water, and high feed-water temperatures could also necessitate specific handling systems, neither of which are relevant in this case.