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Specialists in Electric Hot Water Cylinders

What Is a Tundish? Understanding Unvented Cylinder Components

30 January 2024

Unvented cylinders offer reliable performance, peace of mind, and the steady stream of hot water you need at every tap in the home. However, because it’s a sealed, pressurised system, safeguards must be put in place to help prevent potential problems. One of those safeguards is called a “tundish”. What is it, and what does it do?

What Is a Tundish?

Technically speaking, a tundish is nothing more than a special type of pipe fitting. You’ll find them on unvented cylinders but also on boilers and other pressurised systems, where it’s important that you can check for leaks.

What Does a Tundish Do?

A tundish serves several different purposes. It connects the overflow pipe to the drainpipe, for one. For another, it provides a window on the operation of your unvented cylinder. You can think of the tundish as a viewport or window: it allows you to see if water is flowing from the overflow pipe into the drainpipe.

Why Is a Tundish Important?

The tundish on your unvented cylinder is a critical piece of equipment. By allowing you to see if water is flowing between the overflow pipe and the drainpipe, it alerts you to a potential overpressure situation. The overflow pipe on your unvented cylinder connects to the pressure relief valve. This valve is designed to open only under specific conditions, such as when the internal pressure within the cylinder becomes dangerously high. It opens to allow excess pressure, steam, and water out of the cylinder. Checking the tundish should be part of your regular maintenance.

What Should You Do If You See Water Flowing in the Tundish?

If you check your tundish and notice water flowing through it, call a G3-certified plumber immediately. This is a sign that your unvented cylinder has experienced an overpressure situation, causing the pressure relief valve to open. Your cylinder must be inspected to determine what is causing the situation, and repairs should be made to prevent the situation from reoccurring or growing worse.

Choosing to do nothing will result in some potentially serious consequences. The least of these is wasted water, which increases your resource consumption and costs. In some instances, escaping water can spill out onto the floor coverings, which will cause damage over time. If the damage is severe enough, you’ll need to replace the floor coverings and potentially the subflooring, too.

Finally, this also exposes the cylinder body to repeated overpressure situations. That stresses the metal and leads to fatigue. In severe situations, it can ultimately cause your cylinder to fail catastrophically.

At EasyFlow, we understand that it’s easy to overlook something as seemingly minor as a few drips of water within your tundish. That’s why we offer annual maintenance plans. Our G3-certified plumbers will inspect, service, and maintain your cylinder to ensure that you never have to worry about overpressure situations or the resulting damage. Our goal is to provide you with complete peace of mind – call us today to schedule your maintenance!


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