Features and Benefits of the hotun dry trap tundish

Unvented Water Heaters

There are many features and benefits of the hotun dry trap tundish that make it an industry go-to product. It is now available in over 80% of Britain’s Plumbing Merchant Outlets

A (brief) overview history of the hotun dry trap tundish


(for a more detailed history please click and view the “hotun journey”)

The inventor of the patented hotun dry trap tundish a picture of Russell Armstrong

Russell Armstong – Mciphe, professional plumber and HVAC design engineer


The hotun dry trap tundish was invented by, Russell Armstrong, a professional plumber and HVAC design engineer, back in 2013.


He was working on a job that needed a tundish with an air break to drain AND a way of stopping smells and odours coming back up out of a macerator.

There was a limited choice of products existing at the time. Standard tundishes don’t have any form of in-built trap. There were self-sealing membrane traps but the combination of the two did not work. It was too big and bulky.Worcester Bosch Technical Bulletin TB0107B using hotun dry trap tundish method for combined PRV and Condensate discharge

There had to be a better way. Russell couldn’t find an existing product so was inspired to invent one!

hotun was launched in April 2015 and had its show launch at the Installer show in 2016

Roughly 4 or 5 weeks after hotun was successfully rolled out to the British market, Worcester Bosch became interested. As a result, they, and then other boiler manufacturers, accepted the hotun dry trap tundish for use with their boilers. They gave the official green light to run the PRV, via the hotun dry trap tundish, to an internal drain point of discharge.

Worcester Bosch was the first boiler manufacturer to sanction this method of installation and in 2016 the subsequent Technical Bulletin TB 0107 was published! A momentous and very positive moment for the future of hotun.

Before hotun came along, boiler manufacturers insisted that the PRV pipe was run in solid pipe to external or discharge to a temperature-rated condensate pump.

In this way, hotun has become an industry game changer and will forever be the product associated with this method of installation. hotun has and is an industry revolution (much as the Adey Magnaclean is now intrinsically linked and associated with magnetic filtration!)

What does hotun do and why do we want to use it?


Small unvented water heaters

Small water heaters (10 – 15 litre capacity) are generally located in internal, landlocked spaces and in kitchen base unit cupboards. Thus the water heater will have limited access to an external wall. For an unvented cylinder, this gives the installer a problem of running the pressure relief discharge to a safe point of discharge.

The regulations state that this pipe be run to an external point of termination and as the pipe is not able to be run then how does the installer solve the problem?

If the installer runs the pipe to an internal waste, several regulations kick in, they are;

Regulations applicable for compliance image - Building and Water Regulations title pages

  • The discharge must be visible and the user of installer must be able to see any water dripping (water regulations undue consumption clauses)
  • If the installer wants to connect the PRV to drain and if it is connected to a potable water source (the water heater), there must be provided a way to prevent either back flow or back siphonage of the water from the waste pipe contaminating the water connected to the water heater (water regulations prevention of contamination clauses)
  • As there must be a visible gap in which to see any water dripping, that gap must be open-sided (not clear solid plastic). There must be provided a device to prevent any odours and gasses from coming back out of the waste pipe and back into the building (Building regulations)

To get round these issues, it has or rather had become common practice for the installer to “hard pipe” the PRV to drain, compromising and therefore breaking the regulations on two fronts,

  1. There is no air gap, so water cannot be seen
  2. There is not protection against backflow or back siphonage contamination

So, if that the is the case then why do installers use this method?

A hard piped installation draws no attention to itself. If a standard tundish was used to solve 1 & 2 above, they then haven’t covered how to stop smells, which would be noticed!

What is the solution?


The hotun® dry trap tundish is the solution


Typical Installation Diagram-Small Unvented Water Heater-hotun 100C

Key features and benefits of the hotun dry trap tundish

In one clever little product it provides:

  • An air break to drain
  • Visibility of water passing
  • A sprung valve which prevents odours (easily cleaned (if necessary) in situ in seconds without having to remove the tundish from the pipeline)


#seePRVeasily feature of hotun

Unique Selling Points (USP’s)


  • hotun’s unique design means that any water either dripping or having dripped, is easily seen giving unrivalled and easy visibility to see and therefore diagnose any issues
  • industry beating air break to drain design. Meaning that it is fully WRAS approved to provide the correct level of backflow and back siphonage protection. In turn this means that all possibility of contaminating the potable water is eliminated
  • A patented, sprung valve arrangement to reliably prevent any smells or odours coming back into the building and is now warrantied for 10 years (if registered at time of installation)
  • In pipeline service and cleaning – because of hotun’s open sided construction. If there is any need to clean the valve, it can be done without having to remove the tundish from the pipeline or take the product apart. Simply pull that valve back up through the aperture, clean the rubber diaphragm and then push it back down. This, therefore saves time on any servicing of the product. Other products on the market have to be removed from the pipeline and dismantled for them to be cleaned!
  • hotun is the only dry trap tundish on the market to do all these things in one, fully approved product

hotun – It’s not just a tundish