The ideal pressure for most residential boilers should be between 1.0 and 2.0 bar when the heating is on, and between 1.0 and 1.5 bar when the heating is off or the system is cold. For boilers measured in psi (pounds per square inch), the equivalent range is about 12–20 psi when in operation, with 12–15 psi typical for a cold boiler.

Standard Boiler Pressure Ranges

• Heating off (cold): 1.0 – 1.5 bar (about 12 – 15 psi).

• Heating on (hot): 1.5 – 2.0 bar (about 15 – 20 psi).

• Pressure above 2.5 bar (about 30 psi) is considered too high and can put stress on pipes and valves.

Why Boiler Pressure Matters

• Correct pressure ensures efficient heating and prevents problems like overheating or lack of heat.

• Low pressure (<1.0 bar or <12 psi) may prevent heating from working properly.

• High pressure (>2.5 bar or >30 psi) can cause leaks, failure of seals, or trigger safety shut-offs.

Special Note

Always check your boiler manual, as some models may have slight variations in ideal pressure. Pressure needs can also change for larger or multi-story homes, sometimes requiring slightly higher settings.

If in doubt or you see the pressure in the red zone of your gauge, consult a professional.