How do I clean and flush out an underfloor heating system?

Both new and replacement systems (a system where a new boiler is fitted is classed as a replacement system) are required by the Building Regulations1 to be thoroughly cleaned and flushed and a water treatment inhibitor added to protect the system from further corrosion. This is also particularly important where an underfloor heating (UFH) system is added to an existing heating system, to prevent the new UFH system becoming contaminated by water in the older system which may be contaminated with corrosion sediment. For further details of how to do this consult the following guides and code of practice:


  1. Domestic Building Services Compliance Guide
  2. BS 7593 – Code of practice for treatment of water in domestic hot water central heating systems
  3. BSRIA Guide BG29/2012 – Pre-Commission Cleaning of Pipework Systems
  4. BSRIA Guide BG 4/2011 – Underfloor Heating and Cooling