Okay, I think you mean temperature and pressure relief valve (T&P). They release for one of two reasons...temp too high, or pressure too high. Does the boiler have a temperature gauge showing the outlet temp? Unless it's making steam, it's probably not too hot. My guess is you have a failed expansion tank...$30 or so, and you're good. Check the pressures...if it exceeds 20# or so, and it will if the tank is shot, that's why it's leaking.