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Specialists in Electric Hot Water Cylinders

What is a Tundish?

11 Mar 2019

In this article we will explore everything you need to know about what a Tundish is, how to check it and why it could save you a lot of money

Water heating technology has evolved a great deal over the last century or so. We’ve gone from having to manually heat water over an open fire and carrying it in buckets to being able to open the tap and enjoy immediate access to hot water for all our washing needs.

However, if you’re like most people, you know only a little bit about the technology that allows this to happen. Your water cylinder’s operation is likely as little understood as how satellites work with GPS systems. One of the least understood pieces of your water cylinder is called the tundish.

Knowing what a tundish is, what it does, and how to check it are important considerations for homeowners today.

What Is a Tundish?

While it might sound like some sort of pan or dish that is placed under your water cylinder, a tundish is actually something else altogether. It looks a bit like a plastic cup attached to piping on your cylinder. You’ll find it just off the pressure relieve valve and above the discharge piping.

What Does a Tundish Do?

A tundish performs two principle tasks. First, and most importantly, it serves to prevent any sort of cross contamination between an overflow pipe and a drain pipe. It serves as an air gap and provides a visible window into the overflow system, as well. Without the tundish in place, you would not be able to see any water flowing from the pressure relief valve to the overflow drain.

How Do I Check My Tundish?

Checking your tundish is actually very simple and requires no tools or even special training. To do this, simply locate the tundish, which is often easier to do by locating the pressure relief valve and then following the line. Then check the tundish for signs of water passing. If water is being wasted though the tundish it, according to WaterRegsUK, should be dealt with as soon as possible

If there is water flowing into the tundish, then you know that you potentially have one of four problems. Firstly your Pressure Relief Valve might be faulty, leading to cold water discharge. Secondly your Temperature and Pressure Valve might be faulty, leading to hot water discharge. Thirdly the cylinder is in need of an Annual Service, a lack of which is leading to a pressure build-up. And finally there might be another system feeding into the pipework indicating a fault elsewhere. This could be from a separate heating or cooling system.

This information is very important because it tells you that there is a problem and gives you an indication where its located. Of course, there could be more than one type of problem happening at the same time.

The first and simplest problem to rectify is to get your  unvented cylinder serviced so that the pressure does not get too high. You will need to contact a G3 registered engineer to do this for you.

The second potential problem is that one for more of the safety valves have failed. These valves are only designed to open in the event that the system becomes over pressurised or over heated. If it is leaking and the system is not over pressured, then one or both of the valves might need to be replaced. 

You should make checking your tundish regularly part of your basic home maintenance. If you see water in the tundish, it is important to get in touch with Easy Flow immediately as it indicates either an over pressure situation or a failing safety valve.

A point of safety regarding the tundish. All unvented water cylinders should have a tundish fitted and there are a few points to be aware of, these are:

  • The pipe into the tundish should be one size smaller than the pipe out, e.g. 15mm in with a 22mm pipe out
  • The tundish needs to be within 500mm of the safety valves and in the water cylinder cupboard
  • There needs to be a straight length of vertical pipe of at least 300mm after the tundish and before the first bend. This is to stop the affects of hydraulic resistance which would allow the discharged water to back up the pipe and flood
  • The discharge pipe should be made of a suitable material e.g. copper to resist heat, the discharged water could be heated to 95 degrees centigrade under fault conditions
  • The pipe needs to discharge into a safe place

We often see faults with the installation of tundishes, but the one most often encountered is the lack of fall of 300mm before the first bend.

If you would like a qualified EasyFlow engineer to come and check any problems with your Tundish, call us on 0161 941 5571. Please check our locations; Manchester, Liverpool and Chester to see if we cover your area.


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