KNOW THE DANGERS: Un-vented Cylinders & Discharge Pipe Work

08 May. 2019

Written by Neil Marsh MCIPHE RP RHP EngTech

FORTHRIGHT regularly encounters potentially dangerous un-vented cylinders that are a result of poor installation! To install an un-vented cylinder and ensure its safe operation, the installer must have the expertise and skills to do so. This can only be achieved through the exceptional understanding of the regulations and significant related experience…

Unvented Cylinder Are Commonly Installed Wrong! 

What worries FORTHRIGHT more, is the frequency of poor quality installations that we encounter. As of today, several of our customers are having disputes with home builders and/or installation engineers about potentially dangerous un-vented cylinder installations in properties they own! Some of these homes are part of recently built housing estates where numerous un-vented cylinders installations are likely installed similarly. 

These are not isolated cases. There are entire housing estates in the country where un-vented cylinders could be incorrectly installed and is a danger to life and property!

FORTHRIGHT always stresses the importance of hiring a highly skilled, central heating installer to undertake work to your central heating system! Unless you know the associated risks, you would be clueless about the dangers that could be present in your own home.

If you are in need of a central heating installer in Cheltenham, Gloucester or the surrounding areas that you can trust to install you an un-vented cylinder correctly, we are the company to contact.

A Real Danger When Installed Wrong!

Poorly installed un-vented cylinders are a real threat to you and your family. 

If you are buying a new home you, unfortunately, do not have a say in who installed the central heating system. Due to this, we would encourage you to use the services of a skilled and qualified central heating engineer to inspect the installation and boiler of the new property you intend to purchase. This will help reduce the possibility of expensive repair/replacement bills and risks to you and your family.

We visually inspect un-vented boiler cylinders as standard during our boiler services in Gloucester, Cheltenham, Tewkesbury and other areas in which we provide cover. There are several common issues with un-vented cylinders which can potentially be very dangerous.

The video below shows a poorly installed un-vented cylinder can do to a home.

Video courtesy of Plymouth Plumbers 

In such a case, the temperature of the water in this cylinder could be in the excess of 100DegC. God forbid if anyone is in the home or anywhere near it when something like this goes off! An incorrectly installed un-vented cylinder is potentially a bomb waiting to explode!

How A Correctly Installed Boiler Heated Unvented Cylinder Should Look Like:

Given below is what an un-vented cylinder installation should look like.

You can click here to find the components that commonly will be found close/attached to an un-vented cylinder:

Safety Measures:

There are multiple factors that an un-vented cylinder installation must meet to ensure its safe operation, but at times some of these aspects are not followed.

Should an un-vented cylinder become dangerous and the safety discharge valve engage, then the discharge pipe (labelled A in the above picture) must be designed and routed in such a way that it takes any high pressure, hot water/steam safely to a place where it cannot harm anybody or cause damage to property.

The manufactures instructions and Part G of the building regulations govern the installation of such systems and the standards stipulated must be followed to ensure the optimum levels of safety are met! Failure to comply with these standards will often result in potentially dangerous installations, or worse you could witness an unvented cylinder exploding!

The Discharge Pipework Must Be Right!

FORTHRIGHT can not stress enough about how important the DISCHARGE PIPEWORK is! No matter how poor the installation or what practices have not been followed, so long as the discharge pipework and the safety valves are correctly installed the risk of an un-vented cylinder being a danger to property and life will be minimal.

FORTHRIGHT regularly finds installations where the pipework is not sufficient and presents a real risk! Discharge pipework is the last line of defence, should your cylinder be subjected to high levels of pressure from being overheated. When this happens the pressure release valve on the cylinder will discharge high pressure, hot water/steam into the discharge pipework. If the pipework is not suitably sized, routed, unrestricted along its length and/or not of the correct material there is a risk that this water will enter the property. If the flow of water exiting the cylinder is restricted you may just get an explosion like the one in the video!

Plastic Discharge Pipes

A common factor that we have seen in houses built from 2008 is that many contractors hired to install un-vented cylinders have used solvent weld plastic pipe after the tundish and this is then run into a soil pipe. Ultimately it is used to reduce the amount of work/materials used.

Below is an example of an installation we attended which was completed in 2008 by a plumber in Gloucester. We noticed this whilst undertaking maintenance on the central heating system:

THIS IS NOT ACCEPTABLE! Most solvent weld pipe is not capable of withstanding the temperatures that an unvented cylinder can produce. Should this cylinder undergo a catastrophic discharge (high temperature, hot water discharge) then this pipe will melt and scalding hot water/steam could flow into the property! Push-fit waste pipe may be used and some specific types of solvent weld, but this must be done so very carefully.

The installation above not only used incorrect materials but failed to follow good practices!! NHBC published a document in 2008 explaining the use of push fit waste pipe and its correct installation. FORTHRIGHT strongly advises that suitably sized metal being used and this is terminated at a low level outside the building somewhere remote. 

Incidents Due To Poor Installation

There have been several instances of poor un-vented cylinder installations, one involved a young baby. Discharge pipework, which was not suitable, failed during a cylinder discharge and scalding hot water poured through the ceiling onto the infant, which resulted in the death of the child.  

Repairing damage to a home can be a very stressful and costly, but nothing can be worse than the loss of life! By using so-called installers who do not conform to standards, you are at risk!

Use The Right Installer!

Do not let the price always be the most important factor when deciding on quotations left by installers. Often by taking more care and some extra time you can weed out poor quality installers. Sometimes you may have to pay a little more for the installation as quality engineers will not cut corners. More often than not it will pay for itself in the long run as poor quality work results in additional work being required in the future!

For further advice on how to differentiate between a professional and poor installer, click here!

If an unvented cylinder has to undergo a catastrophic discharge (high pressure, hot water discharge), poor installation is likely to be the cause. The probability of several layers of correctly installed safety measures failing simultaneously is highly unlikely. An un-vented cylinder should undergo regular maintenance to ensure components are free from faults and the cylinder is working safely and efficiently.

Part G of the building regulations governs the installation of un-vented cylinders, the latest and previous version can be found here:

2010 Edition

1992 with 2000 Update Edition

FORTHRIGHT is a professional plumbing and heating company, should you be looking for a heating engineer, gas engineer or plumber in Gloucester, Cheltenham, Tewkesbury, Stroud or the surrounding areas, then look no further!