What Is A Tundish?

A tundish is an essential safety fitting in UK domestic hot water systems — particularly unvented cylinders connected to boilers — that provides a visible air gap and allows homeowners or landlords to spot any discharge from pressure or temperature relief valves before water reaches the drain.

If your tundish is dripping continuously or you are upgrading an unvented hot water system during a boiler replacement, request a new boiler quote from Boilers 2 Go today — their Gas Safe engineers can ensure compliant installation of modern cylinders and safety components tailored to your home or rental property.

What Is A Tundish?

A tundish is a small, funnel-shaped plastic fitting (usually transparent or with a clear viewing window) installed on the discharge pipework from a pressure relief valve (PRV) or temperature and pressure relief valve (TPRV) on an unvented hot water cylinder.

How Does A Tundish Work?

A tundish works by creating an open air gap between the safety valve outlet and the downstream drain pipe, allowing any escaping hot water or steam to be seen clearly while preventing backflow or cross-contamination between the overflow and foul drainage systems.

Why Is A Tundish Required In Unvented Hot Water Systems?

A tundish is required in unvented hot water systems to comply with UK Building Regulations Part G3, providing a visible indication of discharge so faults like excessive pressure, overheating or failing safety valves can be spotted quickly before serious damage or scalding risks occur.

Where Should A Tundish Be Installed?

A tundish should be installed vertically, as close as possible to the safety valve (typically within 500–600 mm), in a visible and accessible location — often inside the airing cupboard or near the cylinder — with a minimum 300 mm straight vertical drop below it before any bends in the discharge pipe.

What Should You Do If Water Is Coming Out Of The Tundish?

If water is coming out of the tundish, it indicates a fault — usually high system pressure, a failing expansion vessel, faulty pressure relief valve or thermostat issue — and you should isolate the system and call a qualified Gas Safe registered engineer immediately to diagnose and repair.

How Does A Tundish Improve Safety For Homeowners And Landlords?

A tundish improves safety for homeowners and landlords by offering an early warning of problems in the hot water system, helping prevent scalding, water damage or legionella risks while ensuring compliance with legal requirements for safe hot water delivery in rented properties.

Need A New Boiler Quote?

Upgrading your boiler and hot water cylinder together often includes proper tundish and discharge pipework installation to meet current regulations and deliver reliable, efficient performance. Request a new boiler quote from Boilers 2 Go today for expert system advice, competitive pricing and professional Gas Safe installation that protects your home or rental investment.

FAQs

Is a tundish required for vented hot water cylinders or combi boilers?

No, a tundish is not required for vented (gravity-fed) cylinders or combi boilers because they do not operate under high mains pressure and lack the same safety relief valves found in unvented systems.

What material should a tundish be made from?

A tundish should be made from durable, heat-resistant plastic (typically polypropylene or similar) that can withstand hot water discharge temperatures without deforming or corroding.

Can I use a dry-trap tundish to prevent smells from the drain?

Yes, dry-trap tundishes (such as Hotun models) include a non-return valve that stops foul odours or gases from rising back into the property while still allowing safe discharge and visibility.

How often should the tundish and discharge pipe be inspected?

The tundish and discharge pipe should be visually checked during your annual boiler and hot water system service to ensure they are clear, correctly positioned and free from blockages or leaks.

Does fitting a tundish require building control approval?

Yes, installation or modification of a tundish on an unvented hot water system must comply with Building Regulations Part G3 and is usually carried out by a competent person who notifies local building control or works under a self-certification scheme.