How a cylinder heats water
Most cylinders contain a coil of pipe. Hot water from the boiler flows through the coil and heats the stored water around it. Many cylinders also have an electric immersion heater as a backup. Hot water rises, so the hottest water is drawn from the top.
Vented and unvented
There are two main types:
| Type | Fed from | Pressure | Notes |
|---|---|---|---|
| Vented | A cold water tank in the loft | Lower, depends on tank height | Simple, common in older homes |
| Unvented | The mains water supply | Mains pressure | Needs a qualified installer and regular checks |
Vented and unvented cylinders compared
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Size and maintenance
Cylinder size depends on household size and bathrooms. Unvented cylinders have safety devices that should be checked regularly by an engineer qualified to work on them, often at the same time as the boiler service.
