Boiler water level control overfilling ?

Hi- My boiler has a safeco boiler water level control. If my heat is on for too long the water level control kicks in and overfills my boiler. (the water level in the glass tube fills over the top of the tube). Then my heaters all start to hiss excessively. The only way to stop this process is to to cut off the water supply to the water level control and shut off the heat, then drain out the extra water. Can I adjust the water level control to not fill so much?