You’re likely to benefit from an unvented hot water cylinder if your showers are weak, you have two or more bathrooms that get used at the same time, a combi boiler struggles to keep up, or you’d like to get rid of cold water tanks in the loft. An unvented cylinder stores hot water at mains pressure, so several outlets can run together with good flow.
The key requirement is good incoming mains pressure and flow, which your installer should measure first. Our unvented cylinders page explains how we assess and install them.
Signs your home would benefit
- Showers that trickle, particularly upstairs on a gravity-fed system
- Two or more bathrooms, and a combi boiler that can’t supply both at once
- Mixer showers that are hard to balance because hot and cold pressures differ
- Old, rusty loft tanks you’d like removed
- A noisy or failing shower pump
- A loft conversion planned, where tanks need to go
Unvented cylinder vs combi vs vented tank
| Unvented cylinder | Combi boiler | Vented cylinder | |
| Pressure | Mains pressure | Mains pressure | Low (gravity) |
| Several outlets at once | Good | Limited | Limited pressure |
| Stored hot water | Yes | No | Yes |
| Loft tanks | No | No | Yes |
| Best for | Larger homes, multiple bathrooms | Smaller homes, one bathroom | Low mains pressure areas |
When it isn’t the right choice
- Low mains pressure or flow at the property
- Small households with one bathroom, where a combi may be simpler
- No suitable route for the safety discharge pipe
- Older pipework that may not handle mains pressure without upgrades
What installation involves
- Measuring mains pressure and flow
- Sizing the cylinder for your household
- Fitting the cylinder with its safety devices, expansion vessel and pressure-reducing valve
- Running a discharge pipe to a safe termination point
- Removing redundant tanks and pipework
- Commissioning and notifying Building Control
The installer must be qualified to fit unvented hot water systems.
Annual checks
Because an unvented cylinder stores water under pressure, its safety devices should be checked every year. This is usually done alongside the boiler service and is often a warranty condition. See our service and repair page.
Unvented cylinders in New Forest homes
Around Ringwood, Lymington, New Milton and Christchurch, many larger family homes and extended properties have outgrown a single combi boiler. Where mains pressure is good, a system boiler with an unvented cylinder is often the answer. Our guide on the best boiler for multi-bathroom homes goes into this in more detail.
Frequently asked questions
What size cylinder do I need?
It depends on the number of bathrooms and people. Your installer should size it based on how your household actually uses hot water.
Can I still have hot water if the boiler breaks down?
Most unvented cylinders have an electric immersion heater as a backup, so you can still heat water if the boiler is out of action.
Does an unvented cylinder need Building Regulations approval?
Yes. It’s notifiable work under Building Regulations and should be installed by a qualified installer who can self-certify or notify Building Control.
Get better hot water
If you’re fed up with weak showers or running out of hot water, give us a call on 01425 542077 or drop us a message and we’ll talk it through with you.