Hot water cylinder and pump installation, including G3-qualified unvented work
Cylinder, Pump and Unvented Hot Water Systems
Cylinder, pump and unvented hot water system work covers installing or replacing a hot water storage cylinder, fitting a pump to boost pressure to showers or taps, and — where the system is unvented, meaning it's fed directly from the mains rather than a header tank — carrying out the installation and any subsequent work under G3 unvented hot water qualification, which is a legal requirement under the Building Regulations.
Definition
What Cylinder & Pump (G3) covers
A hot water cylinder stores heated water for use around the property, either vented (fed from a cold water tank, usually in the loft) or unvented (fed directly from the mains, giving higher pressure without a tank). Because an unvented cylinder is a pressurised system with the potential to fail dangerously if incorrectly installed, UK Building Regulations (Part G) require that unvented cylinders are installed, serviced and repaired only by an engineer holding a valid G3 unvented hot water systems qualification. A pump may also be fitted on a vented system to boost pressure where mains pressure alone isn't sufficient.
Suitable for
- Replacing an old or failed hot water cylinder
- Upgrading from a vented system to an unvented cylinder for higher pressure
- Fitting or replacing a shower or whole-house pump
- Servicing an existing unvented cylinder, which needs annual attention under its warranty terms
Not suitable for
- Unvented cylinder installation or servicing by anyone without a valid G3 qualification — this is a legal requirement, not a preference
- Combi boiler systems, which don't use a separate cylinder and are covered under our boiler services instead
Process
How the work is carried out
- 01
Assessment
Reviewing the existing hot water system, incoming mains pressure and flow rate, and what the household needs from it.
- 02
Specification
Agreeing cylinder size and type, and whether a pump is needed to meet pressure requirements.
- 03
Installation
Fitting the new cylinder or pump, including the safety fittings a G3 installation requires — expansion vessel, pressure and temperature relief valves, and tundish.
- 04
Commissioning and certification
Testing the system and issuing the relevant Building Regulations notification and commissioning certificate for unvented installations.
Typical timescale
A straightforward cylinder or pump replacement is typically completed within a day; an upgrade from vented to unvented, which may need additional pipework and safety fittings, can take a day or two longer.
Cost guidance
Cylinder, pump and unvented hot water system work typically costs £350–£1,200 per job in our area, with a pump replacement at the lower end and a full unvented cylinder installation — including the required safety fittings and G3 commissioning — at the top of that range. We provide an itemised quotation after inspection rather than a fixed headline price.
Limitations and exclusions
- Unvented cylinder installation and servicing is only carried out by G3-qualified engineers, in line with Building Regulations Part G
- Building Regulations notification is submitted for unvented installations as required; we retain the commissioning certificate for your records
- Any electrical supply upgrade needed for a pump is scoped and carried out by a suitably qualified electrician
Areas we cover
Cylinder & Pump (G3) across Sussex, Surrey, Kent and South London
Local property styles, planning authorities and neighbourhood coverage for cylinder & pump (g3) in each town we work in.
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FAQs
Cylinder & Pump (G3) FAQs
What does G3 qualified mean and why does it matter?
G3 is the recognised qualification for working on unvented hot water systems, required under Building Regulations Part G because these systems store pressurised hot water and can fail dangerously if the safety devices aren't correctly installed or maintained. Always check an engineer's G3 qualification before unvented cylinder work is carried out.
Does an unvented cylinder need annual servicing?
Yes, and it's usually a condition of the manufacturer's warranty as well as good practice — the safety valves need checking annually by a G3-qualified engineer to confirm they're operating correctly.
Why would I choose an unvented cylinder over a vented one?
An unvented cylinder is fed directly from the mains, so hot water comes out at mains pressure without needing a loft tank or a pump, which usually means stronger flow at showers and taps. It's a common upgrade where a property has good incoming mains pressure but a low-pressure vented system.
Discuss your cylinder & pump (g3) project
Tell us about the property and what you have in mind, and we'll arrange a site visit.
Last reviewed 2026-07-28.