Never, ever plug the relief valve
As water heats up, it expands with tremendous force—enough to fracture the tank and launch the water heater through the roof (seriously, that does occasionally happen). The temperature and pressure relief valve prevents this by opening if the tank pressure becomes too high. But when a relief valve lets off a little pressure (or just leaks), some homeowners “fix” it by plugging the valve or the pipe connected to it. A very, very bad idea. Boilers also have relief valves, and blocking them is just as dangerous. Have you ever flushed your water heater? You need to ASAP, and here’s how to do it.