Perfect pipes, valves, and fittings for boiler and cylinder installation

Plumber installing hot water cylinder

Which products do you need when installing boilers and hot water cylinders into a home? Here’s our guide to the essential pipes, valves, and fittings you need.

Without a good boiler system, a home would struggle to function. Think of it as the home’s circulatory system, transporting hot water wherever it is needed.

It’s no surprise, then, that installing boilers and cylinders is one of the more complex areas of plumbing and that is exactly why we have detailed the perfect boiler equipment list for professionals.

Be Gas Safe

Let’s start with the legalities. Given the safety requirements and complexities of installation, a variety of skills and legal certifications are needed. Not least is that installation, maintenance, and commissioning must be completed by a Gas Safe registered engineer.

You can refer to the Gas Safe Register website for news on legislation, testing and maintenance too, so you can stay abreast of updates and best practice.

Choosing copper or plastic pipes

One common misconception of boiler and cylinder plumbing is that you cannot connect to them using plastic pipes and plastic push-fit fittings. However, advances in boiler technology means some systems are now compatible with the latest generation plastics.

For example, JG Speedfit PEX and PB pipe, plus selected fittings, are rated to be used within heating systems with working temperatures up to 82°C, and up to 114°C during system malfunction. Many new boilers operate within this temperature range, although you should always check first with the boiler manufacturer.

Alternatively, copper pipework has been the norm in these applications. If the desired finish is in copper and metal, you can achieve this through RWC’s SharkBite fittings. These are made of brass, so they complement copper pipes well in terms of look and feel.

Whether you choose Speedfit or SharkBite, both use the same push-fit principle. These fittings require no soldering or tools to install and can be easily demounted. This makes boiler and cylinder plumbing much easier and faster, especially in tight spaces like airing cupboards.

Installing boilers safely

Once you’ve chosen your pipework, it’s time to select the right safety devices for the installation. Part G of the Building Regulations, section G3, dictates what you need to protect the system in the event of the cylinder overheating or over-pressurising.

There are a number of safety valves to install which safeguard against pressure, backflow and temperature. By installing multiple safety valves, it provides reassurance that if one fails another will provide the safety needed.

Here are the best practices to follow:


The cold feed to a hot water cylinder can be at risk from pressure surges from its mains supply. To avoid this, it is a legal requirement to install a cold water pressure relief valve. This valve acts a safety against this over-pressure from the cold water supply by lifting at a set pressure, discharging water away until the pressure lowers.

The 107 Series Potable Water Pressure Relief Valve from the Reliance Valves range is available in pressures settings from 2.5 – 8 bar – meeting a wide range of settings that are stipulated by cylinder manufacturers.

Reliance Valves, from RWC, provide both the PRV and safety relief valve in one space-saving unit: the Compact Inlet Control Valve. This means you don’t need to fit two separate valves in what could be quite small airing cupboards. Read our guide on push fit valves that every installer needs.

Compact Inlet Control Valve


A double check valve should be fitted to the cold water supply that feeds into it, just in case the hot water expands and goes down the hot water supply and contaminates the water.

Reliance Valves’ Compact Inlet Control Valve also has a check valve integrated into it, so again this helps to save on space.


If the safety relief valve doesn’t kick in and stops working for any given reason, there should be another relief valve installed directly into the cylinder itself to prevent catastrophic damage in the event of overpressure. This type of valve is called a temperature and pressure relief valve. Examples of these are the TPR15 and TPR22 valves from Reliance Valves.

If a temperature of 95°C is exceeded in the cylinder, and the pressure side of the valve has failed, the temperature side lifts to discharge water off the system.

Ambient temperature can also have an effect on pressure within the cold water pipework feeding a cylinder. Therefore, an expansion vessel is fitted to ensure that this does not cause over-pressurisation during normal operation.


Zone valves – the final failsafe

An absolutely final failsafe for cylinder installations is the zone valve. This motorised electrical valve closes in the event of the pressure and temperature relief valve failing.

If the cylinder goes above a certain temperature – typically, this is set to 70°C – the zone valve will kick in and shut the supply off to the tap.

Once all valves are fitted and the cylinder has been installed, the system can start to be filled using a filling loop. By law, this filling loop, which is either a flexi hose or hard pipe, must then be disconnected until the next service. This is also the case of filling loops connected to boilers.

It all boils down to safety and know-how

As all installers should know, boilers and cylinders should never be underestimated. These vital parts of the plumbing and heating system can create serious damage and pose huge hazards if not plumbed correctly.

At RWC, we are committed to ensuring water is delivered at safe and stable pressures and temperature. So, as well as our complete range of pipes, valves and fittings, our technical team is always on hand to provide support and assistance when it comes to boiler and cylinder installations.

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Eric Winter Headshot

Eric Winter

EMEA Director of Product Development [Valves]

About the author

I've had the privilege of being a part of the RWC family for an incredible 25 years.

I joined the company in a technical support role and steadily progressed to become the Technical Director. Throughout my tenure, I've spearheaded the introduction of market-leading products that have revolutionised the industry.

In addition to product innovation, I am a member of WG14 working group, as part of the TC 164 technical committee, which is responsible for revising European and British valve standards. This multifaceted experience has equipped me with a deep understanding of the industry, positioning me as a trusted expert in my field.