Unvented cylinders

Unvented hot water cylinders run off the mains, so where the incoming supply allows it you get hot water at mains pressure without a tank in the loft. We install, service and repair them across Nottingham and Nottinghamshire, for homes and for commercial buildings. The work is notifiable under Building Regulations Part G3 and has to be carried out by someone holding that competence.

How an unvented system works

The cylinder is fed straight from the incoming mains and heated by your boiler, an immersion, or both. Because it is sealed and under pressure, the hot water arrives at the tap at roughly the same pressure as the cold, which is why showers behave better on an unvented system than on a gravity-fed one. There is no cold water storage tank and no open vent.

That pressure is also why the safety devices matter. Water expands as it heats, and in a sealed cylinder it has nowhere to go, so an expansion vessel takes up the extra volume. Behind that sit a pressure relief valve and a temperature and pressure relief valve, both discharging through a tundish to a safe termination outside where a discharge can be seen.

Installation and G3 competence

Unvented work is notifiable under Building Regulations Part G3 and can only be carried out by someone holding the relevant competence. We work to the Part G3 requirements on these systems, and we have trained with Gledhill on their cylinders.

Before quoting we measure the incoming mains flow rate and pressure, because an unvented cylinder can only deliver what the mains gives it. If the supply will not support it we say so rather than fitting something that will disappoint you. We then size the cylinder against how many outlets are likely to run at once, agree the position, and plan the discharge route, which often decides where the cylinder can go.

On the day we install the cylinder, expansion vessel, valves, tundish and discharge pipework, commission the system, set the operating temperatures and test each safety device. You get the benchmark record, we explain what notification paperwork follows, and we walk you through the controls before we go.

Servicing and common faults

An annual service is a requirement of most manufacturers' warranties and is the thing that keeps the system safe. We check and recharge the expansion vessel, test the pressure relief and temperature and pressure relief valves, check the immersion and thermostats, inspect the tundish and discharge route, and check the cylinder for signs of overheating or corrosion.

The fault we see most is water running from the tundish. That is usually a flat expansion vessel, sometimes a passing or failed relief valve, occasionally a thermostat allowing the cylinder to overheat. Other common calls are lukewarm water from a failed immersion or a scaled coil, and noisy filling or pressure loss from a faulty pressure reducing valve.

We diagnose before we replace parts, and we tell you what we have found and what the options are so you can decide. Rates and how we work are agreed with you at the time you book.