Hot water cylinder installation
Vented or unvented, sized for how your household uses hot water.
If your home has a system or regular boiler, the hot water lives in a cylinder. We replace tired copper cylinders, upgrade gravity systems to unvented cylinders for mains-pressure showers, and fit cylinders when people move away from a combi. Unvented work is done by engineers trained and certified for it, and you get a fixed quote before we start.
Vented or unvented?
A vented cylinder is fed by a cold water tank in the loft. Pressure comes from gravity, so showers upstairs can be weak unless you add a pump. They are simple, cheaper to fit and need no annual safety check on the cylinder itself.
An unvented cylinder is fed straight from the mains. You get strong pressure at every tap and no loft tank. It needs decent mains flow, a discharge pipe to a safe point outside and safety controls that must be checked.
- Choose unvented if you want powerful showers, have good mains flow and want the loft tank gone
- Stay vented if your mains flow is poor or you want the simplest, lowest-cost replacement
- Either works with a system boiler or a heat pump (heat pumps need a cylinder designed for them)
Unvented cylinders and the G3 rules
An unvented cylinder stores hot water under pressure, so Part G3 of the Building Regulations sets safety requirements for how it is installed. The installer needs to be competent for this work. In the trade that usually means holding an unvented hot water qualification (what most engineers call their G3 ticket) and being registered with a competent person scheme.
When a scheme-registered installer does the job, they self-certify it and you get a compliance certificate. If the installer is not registered, building control has to be notified before the work starts. Either way, keep the paperwork: buyers' solicitors often ask for it.
Getting the size right
Too small and the hot water runs out halfway through the second shower. Too big and you heat water you never use. We size by the number of bathrooms, how many people live there and when you use hot water, not just by bedroom count.
If you are planning a heat pump, the cylinder needs a larger coil to work with lower flow temperatures. Tell us at the start and we will spec one that suits an air source heat pump later.
Coming from a combi?
Families who outgrow a combi often go to a system boiler and unvented cylinder, so two showers can run at once. Which? puts the cost of adding a cylinder at £350 to £750 for vented and £900 to £1,400 for unvented, depending on size, on top of the boiler work.
For the boiler side of that change, see new boiler cost. We quote the whole job as one fixed price after a survey.
What is included
- Survey including a mains pressure and flow test
- Cylinder sized to your household and boiler or heat pump
- Old cylinder and, for unvented, loft tanks removed
- Unvented safety controls, expansion and discharge pipework fitted
- Building Regulations paperwork for unvented work
- Commissioning and a walkthrough of the controls
Hot water cylinders FAQs
Do unvented cylinders need servicing?
Yes. Manufacturers generally ask for an annual check of the safety valves and expansion vessel to keep the warranty valid. We can do it at the same visit as your boiler service.
What is a G3 qualification?
It is the common name for the unvented hot water qualification engineers take to show they can install and maintain these systems safely under Part G3 of the Building Regulations. Ask any installer to show you theirs.
Can I have an unvented cylinder with low water pressure?
It will only perform as well as your mains supply. We test the flow and pressure on the survey. If it is too low, a vented cylinder with a pump, or a mains upgrade, may be the better route.
How long does a cylinder replacement take?
A like-for-like vented swap is usually a day. Converting to unvented, with new discharge pipework and loft tanks removed, often takes one to two days.
My copper cylinder is leaking. Is it repairable?
Small leaks on fittings can often be fixed. A leak from the cylinder body itself usually means replacement, and it is worth doing before it gets worse and damages the ceiling below.
Get a fixed price for your home
Tell us about the job and we will arrange a free survey.