When a relief valve starts opening and blowing out or dripping water it is not necessarily defective it is doing what is is supposed to do.
So do not replace them right away without troubleshooting.
Oil fired Boilers and furnaces with little red reset button.
Only press button ONE time if unit don't fire troubleshoot or call for service.
Most times, not all, ( you don't know) when you push red reset button unit tries to start but don't you are filling the inside of the unit with oil, now suppose you push button five times and unit fires, Guess What ? All that oil goes BOOM!
Please don't ask me how I know because I don't want to relive stupid mistakes.