You should have a combination water pressure reducing and auto fill valve on then cold water supply to this boiler. Your system should be operating in the 15-18# range! which is what the pressure reducing section is typically factory set at. It is adjustable. That relief valve is a primary safety device. Get someone in who knows what they are doing and get it fixed. Constant addition of fresh water will harm the system over time. As well, it is possible for the precipitant at the mouth of the relief valve to actually seal the relief valve rendering it inop. You then have a bomb in the basement and yes, I do intend to scare you!