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✅ HelpfulWater Supply & Storage
The Hot Water Cylinder
If you have a system or conventional boiler, your hot water is stored in a cylinder — usually in an airing cupboard.
⚙️ Vented vs unvented
Vented cylinder: Fed from the loft tank. Lower (gravity) pressure. Common in older properties. Simpler, fewer safety concerns.
Unvented cylinder: Fed directly from the mains. High pressure — same as your kitchen cold tap. Has multiple safety devices. Must be installed and serviced by a qualified engineer.
🌡️ The cylinder thermostat
On the side of your cylinder is a dial — the cylinder thermostat. It should always be set to 60°C. This is the temperature at which Legionella bacteria is killed. Do not turn it down to save energy.
🛠 What to tell an engineer
"I have a vented hot water cylinder in my airing cupboard — it's not heating up and the thermostat is set to 60°C." The distinction between vented and unvented matters enormously for how a job is approached.
Annual tip: Once a year, run your cylinder at a higher temperature (65–70°C) for a couple of hours to kill any accumulated bacteria — a thermal disinfection cycle. Your plumber can set this up.
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General guidance only — not a substitute for professional advice. Always consult a qualified engineer if you are unsure. Gas work must only be carried out by a Gas Safe registered engineer. Unvented (pressurised) hot water systems must be worked on by a G3-qualified engineer. We accept no liability for any loss, damage, or injury arising from the use of this information.