Restore pressure in a combi boiler?

When you turn the "top up "valve open it wide you can sometimes hear the water going in but the gauge won`t show at once.Have the heating switched on and if it is filling the boiller should flash when it gets around .9mb let it go up to 1.4mb.As it starts topping up start to close it back a little so when you reach 1.4 you can shut it off easy.