My boiler supplies heat and household hot water. I changed the expansion tank and the pressure relief valve last week, and discovered that another valve on the house hot water supple line was dripping. I found out that this valve was called a calibrated pressure relief valve as a back-up valve (in addition to the main pressure relief valve). I am thinking of replacing it with a Watts 530c (1/2"). My question: What psi should I set it?