Vented Cylinder Installation London
Supply, installation and like-for-like replacement of vented hot water cylinders, with honest advice on whether vented is really the right choice for your home or whether another setup would serve you better.
What Is a Vented Hot Water Cylinder?
A vented hot water cylinder is a storage cylinder, usually copper, fed with cold water by gravity from a cold water tank in the loft. A vent pipe lets expansion escape safely back to that tank, which is why it's called "vented". It's the traditional hot water setup in the UK and is still found in a very large number of London homes.
How does a vented system work?
- 1
Cold water tank fills the cylinder
The cold water storage tank in the loft feeds the cylinder by gravity.
- 2
The water is heated
A coil connected to your boiler, or an immersion heater, warms the stored water.
- 3
Hot water is drawn from the top
Opening a hot tap pulls hot water from the top of the cylinder, and cold water refills from below.
- 4
Expansion goes up the vent pipe
As water heats and expands, the extra volume rises up the vent pipe and returns to the cold tank.
Pressure at your taps comes from the height of the loft tank above them, not from the mains. A regular (heat-only) boiler usually sits alongside a second small tank, the feed and expansion tank, which tops up the heating circuit.
Parts of a Vented Cylinder System
Cylinder
Usually copper, insulated with a factory-fitted foam layer or a jacket to hold heat in.
Cold water storage tank
Normally in the loft, positioned above the cylinder so gravity can feed it.
Vent and overflow pipes
Let expansion escape safely and stop the tank overflowing into the house.
Heating coil
A coil inside the cylinder carries boiler-heated water to warm the stored water.
Immersion heater
An electric element, used as the main heat source or as a backup.
Cylinder thermostat
Controls the stored water temperature and tells the boiler when to heat it.
Types of Vented Cylinder
Indirect cylinder
Heated by a coil connected to your boiler. This is the standard choice for homes with a central heating boiler, and it normally includes an immersion heater as backup.
Direct cylinder
Heated only by an immersion heater inside the cylinder. Suits homes without a boiler, or as a simple standalone hot water source.
Fast-recovery cylinder
Has a larger coil so it reheats quicker, which helps in busier households that run out of hot water.
Most domestic vented cylinders are copper. Insulation matters a lot. A well-insulated cylinder holds heat for much longer, and a poor jacket on an old cylinder wastes energy every day.
Benefits and Drawbacks of a Vented Cylinder
Where vented works well
- Simple, proven design that's easy to maintain
- Gentle on pipework because pressure is low
- Quiet in use
- No discharge pipe or unvented safety devices
- Suits weak mains pressure
- Works with a regular boiler
- Some hot water remains from the tank if the mains is off
Where it falls short
- Low pressure at taps and showers
- Shower pumps are often needed
- Needs a loft tank and the space it takes
- Tanks can freeze or leak
- Cylinder must sit below the tank and above the taps
- Heated water can run out in a busy household
Vented or Unvented: Which Should You Choose?
| Question | Vented | Unvented |
|---|---|---|
| Water pressure | Gravity-fed, lower | Mains pressure, higher |
| Loft tanks needed | Yes | No |
| Suits weak mains pressure | Yes | Only if the supply is adequate |
| Installer requirement | Competent plumber | Unvented (G3) qualified |
| Annual servicing | Simpler, fewer safety parts | Expected |
| Best for | Low pressure, regular boiler, gravity setups | 2+ bathrooms, good mains, loft space wanted |
Pressure is the deciding factor for most people. If you have strong mains pressure and two or more bathrooms, an unvented cylinder often gives a better result. If your mains pressure is weak, or your current system works well, vented is a sensible choice and we'll say so.
⚠ Can a vented cylinder be converted to unvented?
No. A vented cylinder is not built to take mains pressure and cannot be converted. To move to unvented you fit a purpose-built unvented cylinder with the required safety devices and take the loft tanks out of use. That's normally done as part of a wider heating upgrade, so it can make sense to plan it together with a new boiler.
What Size Vented Cylinder Do I Need?
Size depends on how many people live in the home, how many bathrooms you have and how you use hot water. This is a starting guide, and we'll confirm the right size at the survey.
| Typical Home | Common Cylinder Size |
|---|---|
| 1-2 bedrooms, 1 bathroom | About 120 to 140 litres |
| 3 bedrooms, 1-2 bathrooms | About 140 to 190 litres |
| 4+ bedrooms or several bathrooms | About 190 to 210 litres |
Bigger isn't always better. An oversized cylinder takes up more of your airing cupboard and loses more heat. The size also has to physically fit the space, so measuring the cupboard comes first.
Vented Cylinder Replacement: How It Works
A like-for-like replacement is often finished in a single day, depending on access and the condition of the existing system.
- 1
Survey
We check the cylinder, loft tank, pipework, vent and overflow, and measure the space.
- 2
Choose the cylinder
Size and type (direct or indirect) matched to your household and your boiler.
- 3
Drain down and remove the old cylinder
The cylinder is isolated, drained and taken out safely.
- 4
Fit and connect the new cylinder
Positioned, connected to the cold feed, hot draw-off, coil flow and return, and vent pipe.
- 5
Replace worn parts
Old valves, immersion heater, thermostat or ballvalve are changed where needed.
- 6
Fill, test and balance
The system is filled, checked for leaks and tested for correct heat-up and thermostat control.
- 7
Insulate and hand over
Insulation is checked, and we show you the controls and what to watch for.
Signs Your Vented Cylinder Needs Replacing
- !
Leaks or damp around the cylinder
A wet airing cupboard or dripping from the cylinder usually means the copper has failed.
- !
Green or white staining
Corrosion on the cylinder or its joints.
- !
Lukewarm water
Can mean a failing coil, element or thermostat, or a worn cylinder that can't heat properly.
- !
Banging, kettling or rumbling
Scale or sludge inside the cylinder or system.
- !
Repeated repairs, or age
Many copper cylinders last 15 to 25 years, so an older one with problems may be better replaced than repaired.
Looking After a Vented System
Vented systems are simpler than unvented ones, but a few checks keep them reliable.
- ✓
Insulate the cylinder and loft tank
A good jacket or foam layer cuts heat loss, and an insulated, lidded loft tank protects against frost and dirt.
- ✓
Check the ballvalve and overflow
A failing ballvalve can overflow or run constantly.
- ✓
Test the immersion heater and thermostat
Useful as a backup, so it should work when you need it.
- ✓
Keep the stored water hot enough
Stored water kept lukewarm raises Legionella risk. Keep the cylinder at a high stored temperature and keep the tank covered. Landlords have a duty to assess and control this risk.
If you have a regular boiler, a yearly boiler service is the easiest way to get the whole system checked at once. Older systems also benefit from a power flush before a new boiler or cylinder goes in.
Thinking of Getting Rid of the Cylinder and Loft Tanks?
Many London homeowners replace a regular boiler, vented cylinder and loft tanks with a combi boiler, which removes all three and frees up the airing cupboard and loft. That works well for homes with one bathroom, but two or more bathrooms used together usually do better with a cylinder-based system.
Combi boiler
No cylinder, no tanks. Best for one-bathroom homes. See combi boiler installation.
System boiler + unvented cylinder
Mains-pressure hot water for 2+ bathrooms. See system boiler conversion.
Keep it vented
A good choice where mains pressure is weak or the current setup works well.
Cylinder Installation Across London
We install and replace cylinders across North, South, East, West and Central London.
Vented Cylinder Installation: Common Questions
What is a vented hot water cylinder?
A storage cylinder, usually copper, fed with cold water by gravity from a loft tank. A vent pipe lets expansion escape safely back to that tank.
How does a vented cylinder system work?
Cold water from the loft tank flows into the cylinder, a coil or immersion heater warms it, and hot water is drawn from the top. Pressure at the taps comes from the height of the loft tank, not the mains.
Is a vented or unvented cylinder better?
Neither is better for everyone. Unvented gives mains-pressure hot water and frees loft space, but needs good mains pressure, a qualified installer and servicing. Vented is simpler and suits weak mains pressure or an existing regular boiler setup.
Can I replace my vented cylinder like for like?
Yes. It's a common job. We match the size and type, connect the existing pipework and check the loft tank, vent pipe and overflow.
How long does it take to replace a vented cylinder?
Often a single day, depending on access, pipework condition and whether the loft tank or valves need replacing too.
How long does a vented cylinder last?
Many copper cylinders last 15 to 25 years, depending on water quality, insulation and care. Leaks, green staining and repeated problems suggest it's near the end of its life.
Can I convert a vented cylinder to unvented?
No. It's replaced with a purpose-built unvented cylinder and the loft tanks are taken out of use, often as part of a wider heating upgrade.
What size vented cylinder do I need?
As a guide, 1-2 bedroom homes often suit around 120 to 140 litres, three bedroom homes 140 to 190 litres, and larger homes 190 to 210 litres.
What is the difference between direct and indirect?
A direct cylinder is heated by an immersion heater inside it. An indirect cylinder is heated by a boiler coil and usually has an immersion heater as backup. Most homes with a central heating boiler use indirect.
Do I need a loft tank with a vented cylinder?
Yes. It needs a cold water storage tank, normally in the loft, above the cylinder. A regular boiler also usually has a separate feed and expansion tank.
Will a vented cylinder give me a good shower?
It depends how high the loft tank is above the shower. If pressure is low, a shower pump often helps. For strong pressure at every outlet, an unvented cylinder may suit you better.
Do vented cylinders need servicing?
They're simpler, but still benefit from checks: the immersion heater and thermostat, the loft tank and ballvalve, the insulation and any sign of leaks.
Can I replace my cylinder and loft tank with a combi boiler?
Often yes. A combi removes the cylinder and tanks and suits one-bathroom homes best. Two or more bathrooms in use together usually suit a cylinder better.
Why is my hot water only lukewarm?
Common causes are a faulty cylinder thermostat, a failed immersion element, a coil that isn't being heated properly, sludge in the system or a worn cylinder.
How much does vented cylinder installation cost?
It depends on the cylinder size and type, whether the loft tank or pipework needs work, access and the condition of the existing system. We survey your property and give you a written fixed quote before any work is booked.
Are vented cylinders being phased out?
Not banned. Unvented is increasingly used in new work, but vented cylinders are still widely installed where mains pressure is weak or a gravity system already works well.
Is there a Legionella risk with a vented system?
Any stored water system carries some risk if kept lukewarm or unused. Keep the cylinder at a high stored temperature, keep the loft tank covered and insulated, and use the system regularly. Landlords must assess and control the risk.
Related Heating Services
Request Your Vented Cylinder Quote
Tell us what you have now and what's going wrong. We'll survey the cylinder, loft tank and pipework and give you a written fixed quote, and we'll tell you honestly if a different setup would suit you better.
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