Open and Closed Heating Systems

The heating and plumbing industry doesn't always use the terms "open system" and "closed system" consistently. For clarification, here is what we mean by "Open" and "Closed" heating systems.

• • Open Vented/Gravity Fed System: a central heating system where pressure for the heating water circuit is maintained by a filler and expansion (F&E) tank, typically found in the loft or attic.

  • Closed/Sealed/Pre-Pressurised System: a sealed central system where pressure is maintained by a closed expansion vessel filled from a loop pipe and there is no tank.

Most of our heating products are suitable for either of the above types of system so long as they are installed in accordance with BS7593 and a suitable corrosion inhibitor/biocide/antifreeze is included in the water at the correct level specified by the product manufacturer. Please see individual products for system details.

Our products should not be installed on obsolete direct hot water systems in historic properties (built pre-1960s) where the same water circulates through both central heating and hot water cylinders, due to the risk of internal corrosion and/or water contamination with inhibitor chemicals.

System icons in our brochures refer to:

O = Open Vented/Gravity Fed

C = Closed/Sealed/Pre-Pressurised

If you have any questions about whether a product is suitable for your central heating system, please feel free to speak directly to our heating technical department on 01908 272447.