Unvented Cylinder and Hot Water Cylinder Installation
If your home stores hot water in a cylinder, its condition matters as much as the boiler's. This page explains the types, the signs a cylinder is failing and what replacing one involves.
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What is an unvented cylinder?
An unvented cylinder is a sealed hot water store fed straight from the cold mains, with no tank in the loft. Because it runs at mains pressure, showers and taps upstairs get strong flow, and several outlets can run together without the pressure collapsing.
A vented cylinder is the older type, usually a copper tank in an airing cupboard fed by a cold water tank in the loft. It relies on gravity, so pressure depends on how high the loft tank sits above the taps. Upstairs showers in particular can feel weak.
Unvented vs vented: which suits you
An unvented cylinder suits most homes with a reasonable mains supply and more than one bathroom. A vented cylinder can still make sense where mains pressure or flow is poor, or where you want to keep the existing setup as simple as possible. Both work with a system boiler installation; our combi vs system boiler guide explains when a cylinder is worth having at all.
Signs a cylinder needs replacing
Cylinders last a long time, but these are signs it is near the end:
Water pooling under the cylinder or green staining on copper joints
Hot water running out much sooner than it used to
Rust-coloured hot water or a metallic smell
A failing immersion heater or a cylinder thermostat that no longer controls the temperature
What installation involves
First the mains pressure and flow are checked, as they decide whether an unvented cylinder will perform well. The cylinder size is matched to your bathrooms and household. If you are switching from vented to unvented, the loft tank and its pipework come out, and the cylinder needs a safe discharge pipe run to a suitable drain.
Unvented cylinders have safety controls, including temperature and pressure relief valves and an expansion vessel. Building regulations require them to be fitted by a suitably qualified installer and notified to building control, and they should be checked every year. Chris will explain who does what for your installation when he quotes.
Replacing a cylinder with the boiler
If the boiler is also old, it often makes sense to plan both together, so the controls, pipework and boiler are set up as one system. We look at this as part of our wider boiler installation service. If your hot water has stopped rather than slowly failing, read no hot water from the boiler first, as the fault may be a part rather than the whole cylinder.
Get a quote
Send a photo of your cylinder, its label and the loft tank (if you have one) to 07429 632804 on WhatsApp, or use the quote form.
Common questions
Hot Water Cylinder Installation FAQs
Clear answers before you arrange a visit.
Can a hot water cylinder be installed outside?+
Normal domestic cylinders are designed to be fitted indoors, where they are protected from frost and weather. Outdoor setups need equipment made for the purpose, so most homes keep the cylinder inside.
Can a hot water cylinder explode?+
An unvented cylinder has several safety devices to stop that happening, which is why it must be fitted correctly and checked every year. Never tamper with the relief valves.
Can hot water cylinders leak?+
Yes. Joints, valves and old copper cylinders can all leak over time. Water under the cylinder or dripping from the discharge pipe should be looked at.
Does an unvented cylinder need servicing?+
Yes. The safety valves and expansion vessel should be checked every year, often at the same visit as the boiler service.
