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Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: February 13, 2024. Updated: February 13, 2024

What Is A Tundish?

What is a tundish? Boilerhut Quick Guide

The tundish plays a critical safety role in unvented hot water systems, which are gaining popularity over traditional heating solutions. This guide will break down what a tundish is, its functions, and the regulations surrounding its installation.

Introduction to Tundish in Hot Water Systems

Unvented hot water systems are directly connected to the mains. This eliminates the need for a cold water tank. They save space and provide consistent high water pressure. However, specific safety components, including a tundish, are indispensable to manage the high pressure within these systems safely.

What Is a Tundish?

A tundish is a component designed for safety and maintenance in unvented hot water systems. It’s a conical device between two piping sections near the cylinder’s temperature and pressure relief valve (PRV).

Featuring a transparent window, it allows for easy monitoring of any leaks. It serves as an indicator of potential issues within the system. The tundish must be installed within 500 mm of the PRV, ensuring it’s in a visible and accessible location for regular checks.

Functions of a Tundish

The primary role of a tundish is to channel water or steam released by the PRV safely. This can happen during instances of excessive pressure within the cylinder.

This mechanism helps maintain the system’s integrity and prevent overpressure scenarios. Furthermore, the tundish incorporates an air break, providing a physical gap between discharge and waste pipes. This prevents backflow and ensures proper drainage.

This air gap is vital for preventing cross-contamination and ensuring wastewater is appropriately directed away from the system.

Applications Beyond Heating Systems

Tundishes are useful in various systems beyond heating, including air conditioning units, refrigeration, and wet room drains. They facilitate the proper drainage of condensate or wastewater. Incorporating an air gap helps prevent backflow and blockages.

Regulatory Compliance for Tundish Installation

Installation of a tundish must comply with specific building regulations. Proper placement is crucial. The tundish must be positioned no more than 500 mm from the PRV and ensure a minimum of 300 mm straight drop below it for effective discharge.

Compliance with these regulations ensures the tundish functions as intended.


The tundish is an essential component of unvented hot water systems. By allowing for the monitoring of discharge and preventing backflow, it ensures the system operates within safe pressure levels and complies with relevant regulations.

Regular checks of the tundish for any signs of leakage can preemptively address potential issues.

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