TN 10321 - Condensate drainage and unvented hot water systems

In the UK, the use of a temperature relief valves or combined temperature and pressure relief valves is mandatory for unvented hot water storage system in excess of 15 litres and also used on some vented hot water storage systems. These valves can discharge at 96?C (BS EN 1490:2011). However, discharges from pressure-only relief valves without temperature control will discharge at over 100?C. The HepVO ® self-sealing valve can be fitted to the discharge of unvented hot water storage systems, primary thermal heat stores and heat interface units allowing them to be connected directly to sanitary pipework provided they are fitted with a temperature relief valve or combined temperature and pressure relief valve.