A Pressurisation Unit is required to keep a sealed heating system pressurised and protect the mains water from contamination. In order for a heating system to work correctly, the pressure needs to remain constant. If the system pressure drops (due to a small leak or bleeding a radiator), the Pressurisation Unit will detect this and automatically top up the system with water. The Pressurisation Unit tops up the heating system with mains water, so the correct level of Backflow Protection needs to be in place to protect the mains supply from contamination. All of Arrow Valves Pressurisation Units have built in Backflow Prevention devices suitable for either commercial or domestic systems.
What Is a Sealed Heating System?
A sealed heating system — also known as a closed circuit system — operates without an open feed and expansion cistern in the loft. Instead, system pressure is maintained by a combination of an expansion vessel and a pressurisation unit. This approach is now standard in most modern commercial and domestic installations, offering improved efficiency and reduced risk of corrosion caused by the continual introduction of oxygenated water.
The Role of the Pressurisation Unit
The pressurisation unit connects the sealed heating circuit to the mains cold water supply. It monitors system pressure continuously and, when pressure falls below a set threshold, automatically opens a valve to admit a small quantity of mains water to restore correct operating pressure.
Because this creates a direct connection between the mains supply and a heating system containing potentially harmful substances — including corrosion inhibitors, antifreeze, and bacteria that thrive in warm water — the Water Supply (Water Fittings) Regulations 1999 require appropriate backflow protection to be installed at this connection point.
Backflow Protection Requirements for Pressurisation Units
Heating system water is classified as Fluid Category 3 in domestic installations and typically Fluid Category 4 in commercial applications where chemical additives are used. Arrow Valves Pressurisation Units incorporate integral backflow prevention devices rated to the appropriate fluid category, removing the need to specify and install a separate backflow prevention assembly.
Domestic and Commercial Models
Arrow Valves manufactures pressurisation units for both domestic and commercial sealed heating systems. Units are factory tested and commissioned prior to despatch, and are backed by a 5-year warranty. Optional on-site commissioning and annual service visits are available to ensure continued performance and regulatory compliance throughout the life of the installation.
Contact the Arrow Valves technical team to discuss the right pressurisation unit for your project requirements.
