The ideal boiler pressure for most domestic boilers typically falls between 1 and 2 bar. When the heating is off, the pressure should generally be between 1.0 and 1.5 bar, and when the heating is on (boiler operating), it should be between 1.5 and 2.0 bar. This range ensures efficient heating system operation and helps avoid problems such as overheating or insufficient heating. Pressures below 1 bar can cause malfunctions, while pressures above 2.0 bar might indicate potential issues like a faulty pressure relief valve. It is important to regularly check the pressure gauge on the boiler to keep it within this range for safety and efficiency.

For industrial boilers, the working pressure range can be different, typically between 12 to 30 PSI, but for residential/domestic use, sticking to the 1-2 bar range is ideal.

If the pressure is outside the recommended limits, you can usually adjust it by adding water via the filling loop or reducing it by bleeding radiators, but for any suspicion of leaks or mechanical faults, a certified engineer should be consulted.

In summary, the safe and recommended boiler pressure for home use is about 1-1.5 bar when cold (off) and 1.5-2 bar when hot (on).