Pressure gauge clock stay very low and when boiler get hot its reach to 3?

My boiler working ok but pressure gauge stays on zero or under 0.5,when I fill bit more water to reach it to 1 bar, after that when boiler on its peak the pressure gauge go to 3.5 bar, even there is no leakage in my pipe work, my question is, 1. Does this affect to my gas bill ?