What Is a Tundish?

James Elston
Written by James Elston
Updated on 16th November 2023
Posted on 15th November 2023
Topic: Boiler Advice
What Is a Tundish?

What is a tundish on a boiler? How does it work & do you need one?

A tundish is a funnel-shaped form of plastic fitting placed on the exterior of the cylinder piping. It is generally installed on the overflow pipes to avert cross-contamination in boilers.

A tundish functions as an air gap and provides a clear visual window to monitor water overflow in a boiler and this guide by Boiler Central will educate you more about a tundish and how it works.

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What Does a Plumbing Tundish Do?

A tundish has two primary functions, the first is preventing cross-contamination when an overflow pipe attaches to a drain pipe with central heating systems that have a hot water cylinder such as a system boiler. The other function of the tundish is to provide an air gap between the two pipes and to give a way to view the water flow.

What is a Hotun Dry Trap Tundish?

A hotun dry trap tundish is similar to an average tundish with the additional feature of preventing any smell, odour, or gases from entering the building from the connection of drain pipes.

The design is similar to that of a common tundish. The inlet is attached to the body in an open-sided way through the two arms.

The differentiation is by the presence of a single-way spring valve. This one-way valve is held with the aid of a light spring. This single-way value is delicate enough and opens by the presence of low quantities of water.

However, it is also firm enough to keep shut against various gasses. The valve’s spring opens to allow the water to flow to the lower discharge pipe before shutting off due to excessive water in the valve. 

How is a Tundish Installed in Accord with the Buildings Regulation Code?

straight tundish made of plastic

Tundishes are used in a variety of places, but they are part of various building regulation codes.

The common usage locations of the tundish are:

  • Discharge tubes of the water heating equipment such as water boilers, hot water cylinders, etc.
  • Drainpipes of unwanted plumbing systems linked with air conditioning of the buildings
  • Gullies of floor wastage
  • Drain removal pipes of evaporative cooling
  • Laundry machines, dishwashers, water filters, or any equipment needing an air gap for their drainpipes

How Can You Check Your Tundish in a Boiler?

Checking a tundish is an effortless and straightforward task with no special training or tools requirements.

Follow the given steps to locate your tundish:

  • Track down the pressure relief valve to track the tundish.
  • Look for any signs of water. If water is present, your valve is leaking. This is an important indicator of issues with the system.
  • Most commonly, the cause is your unvented cylinder having high pressure. You can rectify this by simply altering the pressure of the affected cylinder. Call a professional to do this step to ensure safety.
  • Another reason for the presence of water can be a faulty relief valve. Replace your valve to see if the issue has been solved.
  • Make sure to check your tundish routinely to keep up your home maintenance.

What are the Regulations Followed to Install a Plumbing Tundish?

Installing a tundish is a task that requires expertise and attention. You must hire a professional heating engineer to do the task. A G3-qualified registered plumber is the best option for the task. The G3-approved documents of the building provide further explanation on the instalment of a tundish.

Who is a G3-Approved Plumber?

The Unvented Hot Water qualification is the G3 qualification. This qualification helps the plumber to get knowledge and skills to work with hot water systems such as unvented hot water cylinders. A certificate or an ID is issued to the certified plumber to identify and contact them when required.

How is Your Tundish Installed Following the G3 Building Regulations?

Each country states certain regulations to follow for installing a tundish. Installing a tundish is not a simple task; bringing in a G3-approved professional for installation is recommended.

To install a tundish:

  • Install the tundish in a similar position alongside the hot water system.
  • The tundish should be installed near the outlet opening of the water pressure or high temperature relief faucet (maximum distance to be 600mm). 
  • Associated equipment such as the water heater and the tundish should be installed in such a placement so that the air gap can give the proper view of the flowing water.
  • The discharge tube collecting water from the tundish should be lengthened vertically (minimum 300 mm) from the tundish before any bends or curve in the discharge tube.
  • It should be ensured that the discharge pipework is made of suitable materials, i.e., steel, so they can resist high temperatures.
  • The size of the discharge pipework should be a size bigger than the average size of the water pressure relief valve.
  • Place suitable warnings to specify the opening of the valve. The pipes should also be pointed to avoid the connection of any sanitary appliances.

If you have a condensing boiler with other waste pipes such as a boiler condensate pipe don’t confuse this with any dripping or leaking pipes as this is supposed to remove wastewater.

How is the Tundish Serviced and Maintained?

A G3-certified professional must perform the yearly maintenance and service to check the tundish for proper functioning. Any limescale build-up should be removed immediately to ensure smooth functioning.

For the hotun dry trap tundish, the professional should pour some water into the hotun to evaluate the trigger point operation.

Want to remove the need for a tundish? Why not convert to a combi boiler? Check out the best combi boiler guide here all of which you can get a quote for if you want to remove your hot water tank and change to a combi boiler, all online in minutes.


A tundish is essential when it comes to ensuring the safety of water as it helps with the prevention of contamination. It is a part of various building codes; however, a tundish should always be installed by a professional to ensure proper installation. If you are looking for long-term usage, you should get it maintained regularly.

Written by
James Elston
James Elston Director Of Boiler Central
Posted on: 15th November 2023
Topic: Boiler Advice

James Elston is our resident boiler replacement and heating expert here at Boiler Central. With over 20 years experience in the boiler installation industry, James ensures that he knows everything there is about our Gas Safe boiler installations, energy saving and home heating solutions. This can be from simply procuring the latest best combi boilers, to reviewing and ensuring that Boiler Central maintains the highest standards across our boiler installation company.

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