The Hot Water Association (HWA) is reminding heating engineers of the importance of regular servicing of unvented hot water storage cylinders. It says that whether unvented systems have heat pumps or boilers, or they are stand-alone unvented cylinders, ensuring safety, system efficiency and warranty compliance is essential.
“Unvented hot water cylinders are not fit-and-forget,” says Kevin Lowe, Technical Manager at the HWA. “These systems operate under high pressure and include several key safety components that need regular attention.”
The HWA advises that servicing should be carried out at least annually by a competent person, ideally someone with a valid G3 qualification. Manufacturers commonly make regular servicing a condition of warranty, and homeowners must be able to provide documented proof of maintenance, usually via Benchmark.
Key checks during cylinder servicing include:
– Manually operating safety valves such as the expansion relief valve and temperature & pressure relief (T&P) valve to ensure they function correctly and are free from limescale or debris.
– Inspecting the discharge pipework to confirm it is not obstructed and allows water to flow freely in the event of a pressure release.
– Testing the pressure reducing valve to ensure it is still calibrated correctly and maintaining safe operating pressure.
– Checking the expansion vessel or internal air gap to confirm it still has the correct charge or volume to accommodate thermal expansion.
– Monitoring overall system pressure to detect potential faults before they lead to failure.
Failure to carry out these checks, says the HWA, can result in valve malfunction, uncontrolled water discharge, and system damage, which may lead to repairs and voided warranties.
The HWA also strongly advises the use of genuine replacement parts. “Only genuine parts are tested and certified to perform safely within the system they’re designed for,” Kevin Lowe warns. “Installers should source replacements from the original manufacturer wherever possible or their designated spare parts stockists.”
The HWA provides guidance and resources on best practice for servicing unvented cylinders, including a detailed servicing guide available on its website: https://www.hotwater.org.uk/uploads/5C47186993739.pdf
