The ideal boiler pressure is often marked as a range in green on the boilers pressure gauge, with the normal boiler pressure being between about 1-2 bars. When the heating is turned on, the pressure on the boiler should be between 1.5 and 2.0 bar, and between 1.5 and 1.8 bar when the heating is off. The usual cold pressure of a boiler should sit at about 12psi (pounds per square inch), but the optimal pressure range may vary depending on the model of the boiler. If the pressure gauge needle sits much outside the green zone, particularly on the high side, there may be a problem. In summary, the ideal boiler pressure range is between 1-2 bars, but its important to consult the manual that came with the boiler or a professional to determine the optimal range for a specific model.