Unvented hot water
cylinders.
Mains-pressure hot water for homes with more than one bathroom. Fixed installed prices online, plus annual servicing and repairs.
What is an unvented cylinder?
An unvented cylinder stores hot water and is fed straight from the cold water main, so there is no cold water tank in the loft. Hot water comes out at close to mains pressure, which means stronger showers and taps that fill quickly, even when two are used at once.
Because the water is stored under pressure, the cylinder has safety valves and a discharge pipe. It must be installed by an engineer qualified for unvented hot water systems (often called G3) and serviced every year.
Direct or indirect?
Indirect cylinders are heated by your boiler through a coil inside the cylinder, with an electric immersion heater as backup. Most homes with a system or conventional boiler have one.
Direct cylinders are heated by electric immersion heaters only. They suit homes without a gas boiler, for example many flats with electric heating.
See indirect prices or direct prices.
Which size do I need?
- 120–125 litres: 1–2 bedrooms, 1 bathroom
- 145–180 litres: 2–3 bedrooms, 1 bathroom
- 210 litres: 3 bedrooms, 1–2 bathrooms
- 250 litres: 4–5 bedrooms, 2 bathrooms
- 300 litres: larger homes or 3 or more bathrooms
The online cylinder price recommends a size from your bedrooms and bathrooms, and the survey confirms it.
What we check before fitting
- Mains water pressure and flow rate – an unvented cylinder needs a good supply
- The size of the cold water main (often 22mm is needed)
- A safe route for the discharge pipe to the outside
- Space for the cylinder and its expansion vessel
- For direct cylinders, the immersion heater wiring
If anything needs upgrading, it is priced at your free survey before you agree to anything.
Replacing a tank-fed (vented) cylinder
If your hot water cylinder is fed by a tank in the loft, switching to unvented means removing the loft tank, changing the pipework and fitting a discharge pipe. The online price shows the cylinder from its standard price, and the extra work is priced at your survey.
Looking after it
Unvented cylinders should be serviced every year by a qualified engineer, and manufacturers need this to keep the warranty valid. The service checks the safety valves, expansion vessel, pressure settings and discharge pipe.
Unvented cylinder questions
Can I have an unvented cylinder with a combi boiler?
Not directly – a combi heats water as you use it and cannot heat a cylinder. Adding a cylinder usually means changing to a system boiler as well. This is priced at a free survey.
Why is water dripping from the pipe outside?
Water from the discharge pipe (or a tundish near the cylinder) can mean a safety valve or the expansion vessel needs attention. Don’t block the pipe. Arrange a repair, and call us if there is a lot of water or it is very hot.
How long does installation take?
A like-for-like replacement is usually done in a day. Converting from a loft-tank system can take longer, and the survey gives you a timescale.
Who fits it
Work is carried out by one of our approved installation partners, registered for the work involved. Your written quotation names the installer, who your contract is with, and your warranty and workmanship guarantee.