What is the typical boiler system pressure range maintained by an automatic fill valve?

• A. 5-10 psi
• B. 15-20 psi
• C. 20-25 psi
• D. 10-15 psi

Answer: (D)

The main idea is how the automatic fill valve keeps boiler pressure at a level that ensures good circulation and safe operation. In most residential hot-water boilers, the system is designed to run at a low, steady pressure, typically around 12 psi when cold. The fill valve is set to maintain a nominal range near 10-15 psi so the pump can push water through the radiators effectively and the boiler can cycle properly.

If pressure were much lower than this, flow through the heating system would be insufficient and the boiler wouldn’t heat efficiently. If pressure were pushed higher, the system would be closer to its limits and the safety relief or expansion controls would come into play; frequent high pressure can stress components. Therefore, the automatic fill valve is used to hold pressure in roughly the 10-15 psi range, which is the typical operating range for many residential boilers.