How do I know when a water heater's relief valve should be replaced?
Pressure relief valves (PRVs) on boilers, at least in my area, are usually 30psi. Normally systems run at about 20psi hot and are set to 12-15 psi cold. Your first step is to determine what your system pressure is supposed to be. Then determine what your system pressure is. If it all checks out you need to change your PRV. They often continue to drip after they start dripping due to sediment build up on the valve seat, so regardless you may need to change it anyway. 15psi PRVs are usually used on steam and you have to be very careful if you are indeed running a steam system as you could easily get burned.