Hot Water Cylinder
Installation & Replacement
London
Unvented and vented hot water cylinder installation by G3-qualified engineers. Megaflo, OSO, Gledhill and all major brands. Survey, fixed-price quote.
Old cylinder failing or losing pressure?
Upgrade to a mains-pressure unvented cylinder for stronger showers and simultaneous hot water throughout your home.
Book a Survey
G3-qualified engineers. Fixed-price quote — no obligation.
Site survey — fixed quote within 24 hours
Specialist Unvented Cylinder Installation in London
RARE Plumbing London specialises in the design, installation and replacement of unvented hot water cylinder systems across London. Our G3-qualified engineers assess cylinder sizing, incoming mains flow and pressure, boiler output and simultaneous hot-water demand before specifying an installation.
Unvented Cylinder Specialists
Brand-specialist installation of Megaflo, OSO, Gledhill and all major unvented cylinders, commissioned to full G3 standard.
G3 Unvented Cylinder Engineers
Every cylinder installed and signed off by a G3-qualified engineer under Building Regulations Part G.
Cylinder Replacement & Upgrades
Like-for-like replacement of failed or ageing cylinders, or full upgrades from vented to unvented systems.
System Boiler + Cylinder Design
Paired system boiler and cylinder sizing for balanced heating and mains-pressure hot water throughout.
Cylinders for Multiple Bathrooms
Correctly sized cylinders for homes with two or more bathrooms and simultaneous hot-water demand.
Cylinder Sizing & Hot Water Demand
Mains flow testing and demand-based sizing to ensure every outlet delivers full pressure at once.
Real RARE Cylinder Installations
See genuine cylinder and plant room installations delivered by RARE engineers across prime London homes.
Hot water cylinder replacement in London typically costs £1,500–£3,500 for a like-for-like unvented cylinder swap (Megaflo, OSO or Gledhill), and £2,500–£5,000 for a full vented-to-unvented system conversion. RARE's G3-qualified engineers supply, install and commission all major unvented cylinder brands with Building Regulations Part G documentation. A standard cylinder replacement takes 3–4 hours; a full system conversion takes a day. Book a site survey for a fixed-price quote.
Cylinder Replacement Costs
Clear, upfront pricing — no hidden extras. Fixed quote after survey.
Site survey — fixed quote within 24 hours
Indicative Pricing
£1,500–£3,500
Supply, installation & certification included
Fixed-price quote after survey — no hidden extras, no call-out charge.
Indicative Pricing
£2,500–£5,000
Supply, installation & certification included
Fixed-price quote after survey — no hidden extras, no call-out charge.
The Right Cylinder for Your Home
Every London property is different. We size and specify the correct system at a site survey — no guesswork, no oversized systems.
Unvented Cylinder Installation
Megaflo, OSO, Gledhill and other mains-pressure unvented cylinders — powerful, simultaneous hot water to every outlet. G3-certified installation and commissioning.
Vented Cylinder Installation
Traditional copper cylinders for period properties and low-pressure systems, installed with correct venting, feed and expansion arrangements.
Cylinder Replacement & Upgrades
Like-for-like replacement of a failed or ageing cylinder, or a full upgrade from vented to unvented for better pressure and freed-up loft space.
New Build & Refurbishment Installs
Full hot water system design and cylinder installation for renovations, extensions and new-build properties across Central London.
Vented vs Unvented Cylinders
The two systems work very differently — here's how to tell which one suits your property.
Vented Cylinders
A traditional copper cylinder fed by a cold water storage tank in the loft, with hot water supplied at low ("gravity") pressure. Still common in period and listed London properties, and a reliable, lower-cost option where mains pressure is limited or a loft tank is already in place.
- No unvented certification required
- Lower upfront cost
- Suits period & listed properties
- Relies on loft storage tank & gravity pressure
- Weaker, uneven pressure with multiple outlets in use
Unvented Cylinders
Fed directly from the mains, an unvented cylinder (Megaflo, OSO, Gledhill and similar) delivers strong, mains-pressure hot water to every outlet simultaneously — with no loft tank required. Must be installed and commissioned by a G3-qualified engineer under Building Regulations Part G.
- Full mains pressure at every outlet
- Simultaneous hot water — ideal for multiple bathrooms
- Frees up loft space — no cold water tank needed
- Requires G3-qualified installation & commissioning
- Higher upfront cost, better long-term performance
Commercial Hot Water Cylinders
Hotels, serviced apartment blocks, gyms and managed residential buildings need much higher hot water demand than a domestic system can handle. We design, supply and install commercial-grade unvented cylinders and twin/multi-cylinder setups sized for continuous, high-volume demand across communal buildings.
- Twin and multi-cylinder configurations for high simultaneous demand
- Sizing based on occupancy, bathroom count and peak usage patterns
- Plant room installation and integration with commercial boilers or heat interface units
- Ongoing PPM servicing and G3 compliance for managed buildings
Ideal for:
What's included?
Every cylinder installation is carried out by a G3-qualified engineer and fully commissioned before we leave. We issue full documentation at the end of every job.
- Site survey & correct cylinder sizing
- Removal of old cylinder and (where required) redundant cold water tank
- Supply & installation of new cylinder, expansion vessel and PRV
- Connection to boiler, immersion heater and pipework
- Full commissioning: T&P relief valve, PRV, TCO and tundish
- System flush and pressure testing
- Building Regulations Part G documentation issued
- Warranty registration & aftercare support
Brands we install
Why upgrade your cylinder
Stronger, simultaneous hot water
Unvented cylinders deliver full mains pressure to every outlet at once — no more losing pressure when two showers run together.
Reclaim loft space
Removing the old cold water storage tank when converting to unvented frees up valuable loft space.
Fewer breakdowns
A new cylinder with a fresh expansion vessel and correctly set controls means far fewer emergency call-outs.
Heating & Hot Water System Design
A hot water cylinder is part of a system — not a standalone appliance. Before recommending a cylinder, RARE engineers assess the whole property to ensure the cylinder, boiler and pipework work together correctly. We size for your actual demand, not a guess. Most installers replace the equipment and leave. RARE designs the installation around your property.
Property & Demand
- Property size and layout
- Heat requirement (kW)
- Number of bedrooms
- Number of bathrooms
- Number of occupants
- Expected simultaneous hot-water usage
Water System
- Incoming mains pressure
- Incoming mains flow rate
- Existing pipe sizes
- Existing cylinder type & condition
- Direct vs indirect configuration
- Recovery times and boiler output
Heating System
- Existing boiler make, model & output
- Heating zones
- Underfloor heating integration
- Radiator sizing and layout
- Smart controls & weather compensation
- System balancing requirements
Practical Considerations
- Plant-room / cupboard space
- Flue route and condensate arrangements
- Future maintenance accessibility
- Water quality and hardness
- Building regulations compliance
- Warranty registration
System Boiler + Unvented Cylinder — designed together
Many premium London properties — townhouses, mansion flats and homes with multiple bathrooms — need a properly designed combination of a system boiler and an unvented hot water cylinder. The boiler heats the home and re-heats the cylinder; the cylinder stores hot water at mains pressure for simultaneous showers and baths. Getting this combination right means sizing both components together based on actual demand, not installing them in isolation.
Combi Boiler Alone
Heats water on demand without a cylinder. Compact and efficient — ideal for flats and homes with 1–2 bathrooms where simultaneous hot water use is limited.
- No cylinder needed
- Compact footprint
- Best for 1–2 bathrooms
- Limited simultaneous hot water
System Boiler + Cylinder
The boiler heats radiators and re-heats the cylinder. The cylinder stores hot water at mains pressure — delivering simultaneous hot water to every bathroom. The right solution for homes with 2+ bathrooms.
- Full mains pressure at every outlet
- Simultaneous showers and baths
- Ideal for 2+ bathrooms
- Boiler and cylinder sized together
Cylinder Upgrade
Replacing a vented cylinder with an unvented Megaflo or OSO delivers mains-pressure hot water without changing the boiler. Effective when the existing boiler is still serviceable.
- Mains pressure without new boiler
- Removes loft cold water tank
- Faster hot water recovery
- Boiler must have adequate output
Need a new boiler too? See our Boiler Installation & Replacement page
RARE sizes the boiler and cylinder together to ensure reliable heating and hot water for the whole property.
What London clients say
"Replaced our old vented tank system with a Megaflo unvented cylinder — freed up half the loft and now every bathroom has full pressure at once. Excellent work."
James R.
Marylebone
"Fast, clean installation of a new OSO cylinder. The engineer talked us through sizing options and gave us an honest, fixed quote upfront."
Charlotte P.
Hampstead
"RARE handled a full cylinder replacement across one of our managed properties with zero disruption to the tenants. Highly professional throughout."
Estate Manager, W1
Mayfair
Cylinder Installation Questions Answered
Common questions about hot water cylinder installation in London.
Still have questions?Related reading from our Knowledge Hub
Authoritative Sources & References
- SourceHeatrae Sadia — Unvented Cylinder Manufacturer
Heatrae Sadia — The official manufacturer page for Heatrae Sadia unvented cylinders, including the Megaflo range — the UK's leading unvented hot water cylinder.
- SourceMegaflo Eco — High Performance Unvented Cylinder
Heatrae Sadia — Official product specification page for the Megaflo Eco unvented cylinder, covering capacity, heating options and installation requirements.
- .gov.ukApproved Document G: Sanitation, hot water safety and water efficiency
gov.uk — Building Regulations Approved Document G covers cold water supply, water efficiency, hot water supply and systems — including G3 requirements for unvented hot water storage cylinders.
Serving London's most iconic neighbourhoods.
Our engineers are established across prime London — near landmarks including Berkeley Square, Harrods, Eaton Square, Regent's Park and Hampstead Heath.
