TIU - Thermal Interface Unit
What is a Thermal Interface Unit (TIU)?

TIUs form part of a Community Heating Network (CHN) that provides central heating and domestic hot water to individual properties or apartments within a single development.

Traditionally in the UK, housing stocks have been built with individual gas combi boilers located in each apartment. Conversely, across mainland Europe Community Heating Networks – (or District Heating Systems as they were previously known), have long been the solution to provide heating and hot water in large community developments, with a centralised energy centre coupled with a low temperature hot water network.

In recent years we have seen a resurgence of CHN developments in the UK as the available technology improves and becomes more popular in helping comply with current legislation for energy efficiency and reduced emissions. Community heating networks operate from a single energy source (the energy centre) that distributes energy in the form of hot water circulating within a primary network throughout a building or housing development. Each individual house or apartment has a secondary network which is connected to the primary network via a thermal interface unit that heats DHW and space heating water via plate heat exchangers to meet the individual demands of the property.

The Radiance TIU range from Reliance UK offer the perfect solution as they can be adapted to exact requirements when an instantaneous or stored hot water system is required in a Community Heating Network installation.

As a leading supplier to the UK heating industry for many years, we have gained a wealth of knowledge and experience in the design and production of innovative products. The RWC brand is recognised for quality and reliability and our TIUs, created specifically to suit UK systems, have been designed, manufactured and tested to ensure they provide the same high levels of satisfaction and longevity.

We understand that no two project requirements are the same, that is why we provide a dedicated technical and design support service to work alongside you. This enables us to develop custom-built solutions to meet the exacting needs of your project. We won’t just focus on the TIUs, we will ensure your whole system operates as effectively and efficiently as possible to meet every demand.

Our Radiance TIUs are manufactured in the UK ensuring lead times are minimal and deliveries can be made to suit a site’s requirements.

High efficiency solution for community heating networks

  • No requirement for gas throughout the building avoids the cost of testing/regulations for installing gas
  • No requirement for flues saves cost and allows for an aesthetically pleasing building exterior
  • No planning constraints
  • Simple design; reduced maintenance
  • Easily integrated with renewable heat sources if desired (CHP, biomass, heat pump, solar)
  • Ultra-safe well-known technology using only low pressure hot water
  • Individual metering options available, including automatic meter reading or a prepayment meter

Are you looking for a Thermal Interface Unit for your project? Use the form provided below and we can help find the perfect solution to meet your needs.

Why choose Timeflow Washroom Solutions?

Today Britain’s reservoirs are threatened by an ever-increasing demand for water. Risks of shortages and pollution caused by excessive use of water are well documented not only in the UK but in many other parts of the world as well. Wastage can account for almost 20% of total water consumption.

To preserve the future of Britain’s water reserves, water must be managed in an economical and ecologically sound way. Reliance UK has a long history of providing high quality products to meet the changing demands of the marketplace and our range of timeflow valves are the ideal solution for water saving and water control devices. Listed on the Water Technology List, Reliance UK products are also WRAS approved and comply to BSEN816 and BREEAM.

Water Savings Explained

Because of the dwindling natural resources and the high cost of water and waste treatment, it is now clearer than ever that we must change our usage habits in terms of water control. But how much water can a timeflow control really save?

Consider the following example. If we assume that the average person will spend 1 minute washing their hands in a public facility, with an unregulated tap running at 15 litres per minute, that person would use 15 litres of water.

If a timeflow tap was fitted, the person would wet their hands and start soaping during the first run time of 15 seconds, finish soaping without water running and then rinse off during the second run time of 15 seconds. With the internal flow regulator set at 6 litres per minute, in this hand washing scenario the person will have used a maximum of 3 litres. A third or fourth activation would still use considerably less water than the unregulated manual tap.

Flow Regulation

In order to minimise waste and to realise the best possible benefits from the use of timeflow taps, it is important that not only the duration of the flow be controlled but also the rate at which the water is flowing. Most taps in the Reliance timeflow range incorporate an adjustable flow regulator; this comes factory set at 6 lpm (at 3bar) but can be adjusted to give a flow of between 4 and 10 lpm. In addition to this a flow regulator is fitted which is also set to 6 lpm but can be removed if a greater flow is desired.

Anti-vandal = Anti-waste

In addition to the substantial savings that can be realised by something as simple as automatically regulating flow as these taps do, there are also substantial savings to be made from the fact that the valves are vandal resistant.

A common occurrence in commercial properties of all types is for taps to be left running, either by accident or design; sometimes a vandal may also block the drain for added fun and destruction. With a typical manual tap this is done by simply leaving it on. With a timeflow tap the button or handle has to be blocked open or tied with wire or string – more difficult but not impossible.


Two critical considerations when selecting timeflow taps for use in the commercial arena are the speed and ease of maintenance of the products. All of the Reliance timeflow taps are built using a one-piece cartridge principle; this means that only one part needs to be stocked to completely refurbish the inner workings of the tap. This can save an enormous amount of time when servicing the taps as well as simplifying the stocking of spare components.

Timeflow Basin and Bib Taps

The Reliance range of timeflow taps are an ideal solution to control and regulate the use of water for ablutionary purposes in commercial, industrial, and leisure applications and can be used in conjunction with Reliance’s range of thermostatic mixing valves to give a complete temperature and flow control solution.

Timeflow taps have been shown to save up to 60% of the water usage of a conventional tap by automatically shutting off the flow of water after 15 seconds. The cartridge style construction of these taps reduces parts stocking and means that maintenance downtime is kept to a minimum.

If you’d like to find out more about Reliance Timeflow Products you can visit our Washroom Solutions product page or drop us a message using the below contact form.

What Are Vented & Unvented Hot Water Storage Systems?

How Do Vented Hot Water Storage Systems Work?

Within a vented system the cold water is heated either directly from an immersion heater within the hot water cylinder or indirectly via the central heating boiler or solid fuel appliance. A cold water tank is also used to remove trapped air and act as an expansion tank to accommodate the expansion of the hot water during the heating process and the occasional chance of an overheat situation.

As they are relatively simple in their construction and operate at lower pressure, vented hot water cylinders tend to be cheaper than unvented. The biggest challenge is they may deliver a lower pressure of water. The system also takes up more space in the home with the combination of the cold water tank and the hot water cylinder.

How Do Unvented Hot Water Storage Systems Work?

Reputedly devised by an Englishman as far back as 1861, unvented systems are commonplace throughout Europe, South Africa, North America and Australia, although the UK remains one of the last bastions of the traditional low pressure vented system.  However, times are changing. The demands from discerning householders for increased performance, sophisticated taps and showers, and aesthetic styling have produced a growing trend towards the installation of unvented systems in the UK, which will continue to increase in popularity.

The basic difference between the high pressure unvented systems and a traditional low pressure vented system is that we no longer require the cold water storage cistern, open vent pipe or cold feed pipe. Instead, the unvented unit is fed direct from the mains cold water supply via an inlet control group preset to the relevant manufacturers specified pressures. Hot water drawn from the unit is then replenished from the mains supply.

As water expands when heated and there is no vent pipe, the expanded water within the system is accommodated by either an external expansion vessel or, in the case of bubble-top units, an internal air bubble within the unit which is generated when the system is commissioned. To maximise the benefits of the unvented system, a sealed heating system, if applicable, can also be installed providing the boiler used is compatible.

The significant benefits to be gained from the installation of an unvented hot water storage system can be divided into two categories – ‘benefits to the specifier/installer’ and ‘benefits to the householder’:

Specifier/Installer Benefits

  • Choice of location – units can be installed virtually anywhere within the building structure, allowing greater flexibility of house and system design and reducing costs.
  • No cold water storage cistern – reduces pipework. No requirement for tank stand or pipework/tank insulation – reduces costs. Roof space can be utilised for additional living accommodation.
  • Balanced pressures – far wider choice of taps and showers can be used.
  • Quicker to install – reduces pipework and installation costs.
  • Smaller diameter pipework can be used – reduces costs.
  • No shower pump required – reduces costs.
  • Ease of maintenance – no access to roof space required.

Householder Benefits

  • Superior performance – ensures constant high flow rates at all outlets and allows rapid filling of baths.
  • Reduces hydraulic noise in system – no filling of cold water storage cistern.
  • Eliminates risk of freezing and burst pipes in roof space.
  • Eliminates risk of contamination – no cold water storage cistern in roof space.
  • Frees roof space – can be utilised for loft conversions.
  • Energy efficient – reduces fuel costs.
  • Aesthetic looks.

Choosing an Unvented System

From the early unvented systems of the seventies, the continued growth of installations in the UK has now produced the sophisticated, high performance units demanded by today’s householder. The availability of unvented systems from manufacturers in the UK, Europe, South Africa and North America now offers the specifier/installer an unparalleled choice to suit virtually any application.

Manufactured from either copper, glass-lined steel or stainless steel, almost all of the unvented systems available in the UK are supplied with an easy to clean finish. Using inlet pressures ranging from 1.5 Bar to 3.5 Bar, depending on the relevant manufacturer’s specification, and available in both direct and indirect form, today’s unvented systems can be divided into three main categories: bubble-top unit, external expansion units and direct gas- or oil-fired units.

Controls for Unvented systems

As the dominant supplier and pioneer in the development of controls for unvented systems, Reliance’s range of controls incorporates unique features to ensure superior performance: ease of installation, long and trouble-free service, and ease of maintenance and replacement.

Controls used on the majority of unvented systems in the UK fall into two specific groups -‘Functional Controls’ and ‘Safety Controls’:

Functional Controls

Required to protect the mains water supply from contamination and the unvented unit from over pressure, these controls consist of the following components:-

  • Line Strainer – filters debris from the water supply to reduce the risk of damage to downstream controls.
  • Pressure Reducing Valve – reduces the mains water pressure to the specified cold working pressure of the unit.
  • Single Check Valve – prevents contamination of the mains water supply from backflow and crossflow between hot and cold distribution pipes.
  • Expansion Valve – protects unit from over pressure caused by failure of pressure reducing valve, failure of expansion vessel or loss of internal air bubble.

Safety Controls

Required to protect the householder and prevent the temperature of the water in the unvented system exceeding 99°C, these controls provide a three tier level of protection.

  • Control thermostat – usually set between 60-65°C.
  • Energy cut out device with manual reset – usually set between 85-89°C.
  • Pressure & temperature relief valve – set to 90°C + 5°C.

Both the control thermostat and energy cut out device are supplied by the manufacturer, the control thermostat offering the first level of protection against over temperature of the water.  The energy cut out device will offer the second level of protection in the event of control thermostat failure.  The energy cut out device must incorporate a manual reset feature and must not be self-resetting.

The pressure & temperature relief valve is the third and final level of protection. Although this valve does incorporate a pressure relief function, the sole purpose of this control is to prevent the system water temperature exceeding 99°C; the pressure relief function is not used.

What Can Reliance UK Offer?

Reliance UK is a division of Reliance Worldwide Corporation, a global leader in water control systems and our products span a wide range of applications including thermostatic controls, valves to regulate water flow and pressure, heating systems and plumbing solutions. All are equally at home in domestic, commercial and industrial applications. Take a look at our Heating System Components, Temperature Control and Flow Control product ranges to see what solutions we can offer you.