The maximum allowable working pressure of a boiler is standard in a residentual boiler.  It is 50 PSI. This standard was established mostly to make all boilers safe to operate since they are in so many homes. As water increases in pressure, the boiling point of water increases as well. When water is heated in a closed system the pressure is also increased. Since there are increases in pressure throughout a boiler system, there was a need to establish the minimum requirement to build a boiler, which is known as the MAWP. The control in a boiler system that ultimately controls the pressure on a boiler system is the pressure relief valve.