Steve Sutton, Technical Manager at the Heating and Hotwater Industry Council, runs through the intricacies involved with upgrading to a sealed heating system.
Sealed systems will include a pump, pressure gauge, expansion relief valve, filling loop, and expansion vessel and, in a high proportion of today’s designs, all these components are situated within the boiler. Happily, this all helps installers by reducing the amount of time and labour needed to fit a new boiler. It also goes some way towards preventing any errors that may occur when selecting or fitting the right components for the job.
Inevitably, technology and regulations move on. Many older appliances that started to be replaced or upgraded to a sealed system in the 1980s used an external filling link, sometimes called a filling loop, comprising a washing machine valve and suitable pipe between the cold water main and heating return pipes to fill the system. A simple solution but, by today’s standards, one that would prove illegal, as it offers no backflow protection to prevent contamination to incoming mains water.
To meet the latest requirements, the pipe is normally a metal braid filling loop containing a double-check valve upstream of the filling loop. This is then connected to either a straight or tee isolating valve, downstream of the filling loop. The components within the loop should also have suitable approval, such as that given by the Water Regulations Advisory Scheme (WRAS).
The WRAS guidance advises that where a closed-circuit heating system has been categorised by the water undertaker as a Fluid Category 3 risk, due to the level of low toxicity, the installation of a compliant double-check valve on the fill point connection to the supply/distribution pipe may be considered as acceptable backflow protection.
Where a fill point connection incorporates a ‘flexible connection’, it is good practice for the hoses on these connections to be completely disconnected and removed when not in use.
A partial disconnection, that is to say only detaching one end of the hose, is equally acceptable, providing that the disconnection is made between the hose and the backflow prevention device on the supply/distribution pipe. The reason for detaching the link is to prevent leaks, assist in preventing over-pressurisation and, ultimately, the potential loss of heating.
A further note added by WRAS advises that if the water undertaker has concerns about the likelihood of contamination, or the suitability of a double-check valve, for example due to either age, operating temperature, or pressure fluctuations, they can require the installation of additional backflow protection.
It should also be noted that some boiler designs include a filling system within the boiler and, as always, manufacturer’s instructions should be followed.
When quoting to install a new boiler with a sealed system, it is also a good idea for the installer to be proactive and inspect the radiator valves already in place, as these are a main source of leaks for pressurised systems. Advising the customer that any worn and leaking valves will need replacing to prevent problems in the future is good practice, and can prevent commissioning issues or a return call to resolve any problems with loss of pressure in the system.
If installers do come across issues with loss of pressure, the first port of call is establishing from the consumer how quickly the system is losing pressure, as well as inspecting for leaks on valves or a pipe tail. If it remains difficult to locate the source of the problem, and you think the fault could be in the boiler, pressurising the system to the correct level, and turning off the boiler isolation valves to the heating system is a further way to check the boiler holds pressure.
Care needs to be taken to ensure that the boiler is disconnected from the mains electricity to prevent operation. If the boiler pressure gauge holds for at least a day, then it’s likely the fault lies within the heating system, not the boiler.
The benefits of a sealed system are wide ranging. Not only do they take up less space, which is a benefit for the homeowner, installation time is also reduced.
Pressuring a system can also help to prevent boiler sounds in the heating system at high temperatures, and can assist with system cleanliness by improving water quality.
As oxygen ingress is reduced, it lowers the potential for corrosion of the system too, such as rusting radiators. However, to ensure effectiveness and efficiency are both maintained over a long time frame, it is still recommended by most boiler manufacturers that a corrosion inhibitor is added to the water, and a system filter should be considered when updating a system to a sealed one.