Safety Relief Valves are last line of defence

Altecnic's Head of OEM Sales (UK & ROI) Mark Mogey lifts the lid on common Safety Relief Valve (SRV) issues...

The safety relief valve (SRV), also known as a pressure relief valve, is principally a safety device and in many cases provides the final safeguard. A SRV is not a process valve or pressure regulator and should not be misused as such. It operates for one purpose only: overpressure protection

SRVs are normally installed in sealed heating systems that include a closed expansion vessel or a hot water cylinder. These valves are used for relieving excess pressure on boilers in heating systems and on stored hot water cylinders in domestic hot water systems. SRVs are also used in solar heating systems and in water distribution systems generally.

If the valve is passing water, then the system has reached the pressure set point of the SRV, so the valve has activated – this is exactly what the valve is designed to do. The most common reasons for activation are an incorrectly sized expansion vessel, incorrect pre-charge setting in the vessel or a failed expansion tank – so there is nowhere for the expansion to go. Occasionally the system pressure may be correct but the valve has activated and has not correctly re-seated. This can be due to a few factors, which include:

• System debris is sitting under the seat, not allowing it to re-seat correctly
• System pressure has not reduced significantly for the seat to drop and is being held open via pressure
• System pressure is very close to set point of the valve; the water can create a valley so water can pass through

In a sealed heating circuit building regulations state, where possible, to install an SRV close to the heat source on the flow circuit. It should be installed in the cold water supply before the water heater, ensuring that there are no other fittings or narrowing of pipework between the water heater and the valve.

To comply with water regulations, valves should not be connected directly to a drain – the discharge should pass through a visible tundish with an AUK3 air gap and be located adjacent to the SRV, to allow vented water to escape. The discharge pipe must be the same size as the valve discharge outlet; must not be longer than two metres; and have no more than two elbows. The SRV should be located at a maximum distance of one metre from the boiler. Due to the high temperature of the discharge, the terminal point of the discharge pipe should be located where sudden discharge cannot cause scalding or injury.

Altecnic Product:

Altenic Caleffi 311 Series
Safety Relief Valve
WRAS Approved.
Altenic Caleffi
313 Series Safety
Relief Valve WRAS








The Altecnic 311 Series and 313 Series (pictured) are high quality examples of WRAS approved SRVs.

For more information, contact Chris Reilly, Country Manager for Ireland, on 00353 85 2152288 or e-mail or Gary Swann, Northern Ireland Sales Manager on 07760 596727 or e-mail or visit the website at