CC-14 – Unvented Cylinder Safety Discharge Detail

Unvented cylinder discharge detail: This drawing shows the safety relief valves, tundish and discharge pipework required for an unvented hot-water storage system.

The system diagram identifies the temperature and pressure relief valve, expansion relief valve and D1 pipework leading to a visible tundish in the cylinder space. No isolating valve or other restriction is permitted between the cylinder, relief valves or discharge route.

The D2 arrangement includes the required vertical drop below the tundish, a continuous fall and pipe sizing based on the valve outlet, equivalent length and number of bends. The external termination is positioned where hot water or steam cannot cause injury or damage. Installation and commissioning must be undertaken by a suitably competent person. For statutory guidance, see Approved Document G on GOV.UK, or explore our related air-source heat pump guide.