Tundishes for Beginners: Everything You Need to Know About Your Cylinder’s Tundish

How much do you know about the components that make up your unvented cylinder? If you’re like most people, it’s not that much. While you don’t need to be an expert, you should know a few things about the most important elements, like the tundish.

A tundish might not be the most exciting part of your unvented cylinder, but it plays a pretty important role in keeping your system safe. If you’ve ever noticed a small plastic or metal fitting with an open section in your cylinder’s setup, that’s your tundish.

But what exactly does it do, and why should you care? In this guide, we’ll walk you through what you need to know.

What Is a Tundish?

A tundish is a safety device installed in the discharge pipe of your unvented cylinder. It lets you visually monitor any water released by the pressure relief valve, helping prevent unnoticed leaks or dangerous pressure buildup. Simply put, if you see water flowing through the tundish, there’s a problem and you need to call for service.

How Does a Tundish Work?

When your pressure or temperature rises too high within your unvented cylinder, the pressure relief valve (PRV) activates, releasing water. The tundish provides a clear gap in the pipework, making sure that this discharge is visible and preventing backflow contamination.

If you ever see water flowing through your tundish, it’s a sign that your system is relieving excess pressure, and that’s something you shouldn’t ignore.

Why Is the Tundish Important?

So, why is the tundish such an important part of your unvented cylinder setup?

1. Early Warning System – If water is flowing through the tundish regularly, it’s a sign of pressure issues, a faulty PRV, or an expansion vessel problem. All of these problems mean that you need to have the cylinder serviced right away.

2. Prevents Backflow – The tundish keeps potentially contaminated water from re-entering your clean water supply. Remember that water within the cylinder can reach any tap in the home, including taps where you draw drinking water. You don’t want contaminated water anywhere in your pipes.

3. Safety Compliance – UK regulations require a tundish in unvented hot water systems for safe operation. Unvented cylinders do a tremendous job of providing mains pressure hot water at every tap, but they do that by creating pressure within the cylinder. If it becomes over pressurised, there needs to be a way to relieve the pressure.

When Should You Be Concerned?

Seeing an occasional drip from the tundish isn’t usually a problem, but constant water flow means something is wrong. The most common issues include:

• A faulty pressure relief valve that won’t close properly.

• An over-pressurized system due to a failed expansion vessel.

• Limescale buildup preventing proper sealing.

What to Do If Your Tundish Is Discharging Water

1. Check the pressure gauge on your cylinder—if it’s too high, you may need professional help.

2. Listen for unusual noises from the cylinder, which could indicate overheating.

3. Call a professional if water flow is consistent—it’s a sign of an underlying issue that needs fixing.

Don’t Ignore a Leaking Tundish

Your tundish is a built-in warning system—if it’s showing signs of trouble, don’t wait for the problem to get worse. EasyFlow can diagnose and fix any issues with your unvented cylinder, ensuring your heating system stays safe and efficient. Contact us today for expert help!