http://media.wattswater.com/es-25aub.pdf . ..."when the pressure exceeds the supply". There is no magical means to relieve the pressure until the house side exceeds the supply, then it can bypass. Until then, it just builds up until something gives, typically the T&P on the WH, or the hoses for the washing machine, or a toilet fill valve. RTFM before you make comments, please.