Central heating pressure

[Brisayshi]

A question about central heating......Is it more efficient to have the pressure in the radiators lower or higher? My boiler will start to work with 0.5 Bar in the system but I think the norm is to have 1 to 1.5 Bar in it. Does water boil faster at a higher pressure or slower because there is more of it? Thanks

[buildersmate]

The technical answer to your question is that water boild at a higher temperature, the higher the pressure.
But this has absolutely no bearing whatsoever on your question since the purpose of a CH boiler is never to actually boil the water.
I should start turning your attention to the playing with the temperature of the thermostat on the CH boiler versus the temperature of the thermostats in the rooms rather than thinking you impact efficiency using the different pressures.

[AlBags]

1 bar cold. Nothing more needed. Much over 1 1/2 bar risks damage to pressure vessel. It will/can show up to around 2 bar hot.