hotun 100 range

hotun 100

Product Overview

The hotun 100 range of products, combines a tundish and dry-trap to provide a safe and visible discharge from a relief valve direct to a local waste or soil pipe, whilst eliminating the risk of foul odours from the foul system entering back into the building.

In a relief valve discharge application, a wet trap would dry out and thereafter allow foul odours back into the building, so is not allowed.

hotun is specifically designed to achieve full compliance with Water and Building Regulations, the hotun dry trap tundish allows a discharge from a relief valve, to connect directly to a foul waste or soil pipe (allowing a flow of water one way, but also providing regulation required, back-flow contamination & back-siphonage protection to prevent cross-contamination of wholesome water & the waste pipe (Category 5 risk water)) provided that the D2 and connecting soil pipe is suitably rated for the appropriate temperatures and flow rates expected when the relief valve is operating under failure conditions.

hotun 100C is WRAS approved –


WRAS Approval Number: 2101323

Specifications - Connections, Flow Rate, Applications

Inlet pipe size


Inlet connection

½” Flat faced tap connector (not supplied)

Outlet pipe size

22mm Cu or 21.5 plastic

Outlet connection

Compression nut and olive (supplied)

Rated flow rate


Max flow rate

16LPM (with optimised flow pipework configuration)

Usual applications

  • Small (<15L capacity) water heaters
  • boilers with PRV’s (unless otherwise stated by a boiler manufacturers specification/instructions)
  • Overflows from storage water tanks
  • Air conditioning unit drip trays
  • MVHR  condensation drip trays
Typical Installation Diagrams

Click either image to enlarge in a new page

Typical boiler installation diagram with hotun 100

Typical small unvented installation diagram with hotun 100


Technical Drawings

hotun 100 Technical Drawing - Dimensions

For a printable PDF version, please click on the link below


Specifications - Connections, Flow Rate, Applications

Inlet pipe size


Inlet connection

½” Flat-faced tap connector (not supplied)

Outlet pipe size


Outlet connection

Suitable for 32mm push-fit or universal mechanical fittings – see compatible connection diagrams below –  (hotun hiflo 100 outlet size is not compatible with solvent weld fittings)

Rated flow rate


Max flow rate

20LPM (with optimised pipework configuration – see optimised flow configuration diagrams below)

Usual applications

(see typical application diagrams)

  • Any/all unvented water heaters with combined T/PRV’s up to the rated flow rate. 
  • Boilers
  • Overflows from water tanks
  • Air conditioning drip trays
  • MVHR condensation drip trays


1. All D2 downstream pipework and soil pipes for unvented hot water heaters (with Combined T/PRV’s) must be suitably rated for water discharging at 90-95°C. 

2. Appliances with PRV’s only (ie boilers and water heaters of less than 15L capacity) do not need a D2 waste pipe temperature requirement

Typical Installation Diagrams

Click on any image to enlarge in new page

Compatible 1 1/4" Outlet Connections

The 1 1/4″ (32mm) outlet on the hiflo version is compatible with either universal compression or push-fit fittings.

Due to the material used in hotun plastic (acetyl) it will not successfully solvent weld, and due to its size, female solvent weld fittings will be too large for the male spigot.

It must also be noted that many solvent weld pipes are not of a sufficient grade (material) and are therefore not suitable to be used in unvented hot water heater D2 discharges when connected to a TEMPERATURE RELIEF VALVE discharge line*.

*NB – this note about the suitability of pipework materials is only relevant to applications that have a TEMPERATURE RELIEF VALVE operating at temperatures above 90°C over several cycles of flow.

For all applications that have a pressure relief valve only (eg boilers and small unvented water heaters) the issue of temperature and volume of water is not an issue and a much wider range of materials will be suitable for use.

If you are unsure of these requirements please feel free to contact our technical team on our contact us page and we will be able to fully discuss these issues with you.

Optimised flow pipework configuration example diagram

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Technical Drawings

For a printable PDF version, please click on the link below


Headline Information - Purpose

To prevent deliberate or accidental contact with potentially scalding water dripping/flowing through the open tundish


hotun shield HS100C is only compatible with the “100” range of hotun tundishes, ie threaded inlet. They are NOT compatible with our SF (Speedfit) range of tundishes

Headline Information - When to use shield

hotun shield is designed to prevent the user from accidentally touching potentially scalding hot water.

It is therefore used on a risk assessment and job by job basis with the installer determining what the risk is (if any) and if there is a justification for fitting the shield with the additional safety that the shield brings

Compatible hotun 100 tundish products

hotun shield (HS100C) is compatible with the “100” range of hotun tundishes, ie threaded inlet.

They are NOT compatible with our SF (Speedfit) range of tundishes



Get In Touch

Registered Address

RA Tech UK Ltd
6 Nottingham Road
Long Eaton, Nottingham, UK

T: 01332 702678



In one simple fitting, hotun solves the problem of compliantly running a PRV valve discharge from a pressurised hot water cylinder relief valve or boiler pressure relief valve to a local waste or soil pipe.

hotun combines a tundish and a non-return valve to make a dry trap tundish which acts as a visible early warning device and prevents foul odours from escaping from the waste/soil pipe.


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