It's time for an update

You've been using your good friend IE for quite some time now. It has been a reliable companion for probably the last 20 years.

Unfortunately, due to technology constantly evolving, we would like to kindly ask you to update your browser to one of your liking from the ones listed below. This will ensure that you're going to have good time on our site. Actually, any site really.

Farewell, Internet Explorer.

What is a tundish?

Installer carrying out work on a boiler in a laundry room

What is a tundish?

A tundish is a device placed close to the pressure release valve that allows people to see if water has escaped the system due to excessive water pressure. Unvented hot water systems hold many advantages over traditional heating solutions, but one disadvantage is that excessive water pressure can damage a boiler if left unchecked.

A pressure release valve is installed to allow water to drain from the system if the pressure rises to dangerous levels, and the tundish allows people to see that this is happening and report the issue to a Gas Safe Registered (GSR) engineer.

What does a tundish do?

A tundish is installed to prevent cross-contamination between an overflow pipe and a drain pipe. Unsanitary water from the drain pipe could theoretically enter the system if a tundish is not installed to block this. The other purpose of a tundish is to provide an air gap through which someone can see if water is flowing from the pressure release valve.

Should a tundish drip?

It is important to call a qualified boiler engineer if your tundish is dripping. This is a sign that either there is a fault with the pressure release valve or water pressure in the system is rising too high. In both cases a qualified engineer will need to inspect the system and resolve the problem.

installer carrying out work underneath a boiler

Do I need to be qualified to install a tundish?

Do not attempt to install a tundish if you are not a qualified heating engineer. The tundish has to meet strict regulations and it is illegal to make adjustments to a boiler system without proper training, as determined by the Local Authority Building Control.

According to the UK government’s G3 Building Regulations for unvented hot water systems, the tundish must be placed at least 500mm from the pressure release valve in a visible position so a homeowner can quickly see if water is dripping from the system.

It is also best practice for the discharge pipe from the pressure release valve to be 15mm and for the pipe carrying the water outside the property to be 22mm. The discharge pipe from the tundish must be vertical and be made of metal or other materials able to withstand hot temperatures.


  • A tundish is a fitting installed on overflow pipes that allows people to see if water is flowing from the pressure release valve.
  • If dripping water is visible in the tundish, a GSR engineer should be called immediately to inspect the boiler.
  • A tundish must meet the guidelines set by the G3 Building Regulations, such as being pressed at least 500mm away from the pressure release valve.

If water is dripping from the tundish, contact your local installer immediately