Pressurised water supplied from a storage cistern tank is pumped via ‘ booster pump’ or mains pressure into the cylinder, the advantages of these un-vented tanks, higher pressures obtainable at sinks and shower outlets also with very good flow characteristics coupled with a balanced cold supply make these systems particularly attractive for showers. Extremely low heat loss from this cylinder and fast recovery (reheat-up) time makes the un-vented tank a must in any solar thermal, heat pump or energy-efficient upgrade.

The un-vented hot water tank is a now a standard installation on any new build or renovation project.

Safety features

Un-vented cylinders come supplied with many safety features, at no time the water temperature should reach 100°c as set down by regulations.

• a thermostat with a max set point of 60°c
• high limiting thermostat with a lockout of 90°c
• electrical immersion element high limiting cut out switch.
• (T+P) temperature and pressure release valve with a designed relief temperature of 95°

Also, the cylinders are supplied with a sealed expansion vessel which must be service annually to ensure working order as these will lose the trapped air rendering the vessel ineffective, resulting in excess pressure generated throughout the system.

An annual service is required, we provide this service which includes

• Standing and working pressure test
• Drain and re-pressurise the pressure vessel
• Inspect and operate the temperature and pressure relief valve
• Inspect and check pressure reducing valve
• Check and operate combi- inlet assembly safety valve

This vessel is the expansion vessel for the hot water tank system, this device plays a key role in the safe operation of your unvented hot water tank, it allows for expansion of hot water [DHW] waters, as the water heats in your tank, the heated volume of water expands up to 4%. Example a 300ltr tank when the water is heated to 60°c the water volume expands by approximately 12litres.

Servicing and maintaining the expansion vessel is very important. Like the tyre on a car loses air and needs pumping up, the expansion vessel also loses the air cushion over time and requires pumping up. If there is no cushion for expansion of heated waters, the expansion will result in excess pressure in your un-vented tank system, causing water to leak from the safety valves.