When inspecting your water heater, you may notice that it has a long vertical pipe on the side. Known as an overflow pipe, it’s an important safety feature. The overflow pipe works in conjunction with the pressure relief valve to prevent the tank from generating too much pressure. For a better understanding of the overflow pipe and how it works, keep reading.

What Is the Overflow Pipe?

The overflow pipe is a vertical pipe on the side of a water heater that serves as a drainage system for excess water. It typically runs from the top of the water heater all the way down the side of the water heater. It’s known as an “overflow pipe” because it drains any water that flows over the water heater.

How the Overflow Pipe Works

The overflow pipe is nothing more than a hollow pipe – typically polyvinyl chloride (PVC) – that’s connected to the top of a water heater. If the pressure inside of a water heater gets too high, some of the excess water will spill out the top of the water heater and drain through the overflow pipe.

Most water heaters have an overflow pipe and a pressure relief valve. Also known as a T&P valve, the pressure relief valve allows excess water to escape. If the pressure gets too high, the pressure relief valve will open. Some of the excess water will then drain through the overflow pipe.

What a Leaking Overflow Pipe Means

If your water heater has a leaking overflow pipe, it’s typically a sign that the pressure is too high. Normally, water shouldn’t drain through the overflow pipe. Water heaters, of course, generate pressure as a byproduct of heating the water. Whether you have a gas or electric water heater, it will generate pressure via thermal expansion. The hot water inside of the tank will expand, but because there’s nowhere for the water to go, it will become pressurized.

Your water heater can only handle so much pressure, which is why it has a pressure relief valve and an overflow pipe. If the pressure rises beyond the pounds per square inch (PSI) for which it’s rated, your water heater may drain some of the excess water through the overflow pipe. Therefore, a leaking overflow pipe is a sign of an underlying problem. In most cases, it means your water heater is generating too much pressure.