Another possibility that I forgot to mention is that the expansion vessel could be undersized - if the EV cannot cope with the amount of hot water expansion in the system it will then have to go somewhere else (the PRV). Comprised of a pressure reducing valve, a pressure relief valve a check valve and filter all included in a single Monobloc valve. Pressure reducing valves are devices which, when installed on a private plumbing system, reduce and stabilise the inlet pressure from the water mains.

The item may be missing the original packaging or protective wrapping, or may be in the original packaging but not sealed. This inlet pressure, in general, is too high and variable for domestic systems to operate correctly. Pressure reducing valves (PRV) are installed in domestic water systems to reduce and stabilise the inlet pressure from the mains supply, which is generally too high and variable for domestic appliances to function properly. The charge in the expansion vessel should be the same as the incoming pressure that is set/ controlled by the pressure reducing valve.This multibloc is comprised of a pressure reducing valve, a pressure relief valve, and an internal check valve. Specially shaped diaphragm to give accurate pressure regulation in response to changes in downstream pressure. Caleffi is a decent make, I understand, but these fellows - well, the safety-release-valves - are prone to allowing a drip through after they've been activated. It incorporates pressure reducing valve, pressure relief valves, check valve, and filter in a single valve design. li>