Fed up with weak showers and slow-filling baths? Cold water tank in the loft taking up space? An unvented hot water cylinder delivers mains pressure hot water to every tap and shower in your home – no pump needed, no tank in the loft, just powerful hot water whenever you need it.
HeatBox installs, repairs, and services unvented cylinders across South London – Bexley, Greenwich, Lewisham, Bromley, Croydon, and all surrounding areas, plus extended coverage to Central London and Wandsworth. Our G3-qualified engineers are certified to work on unvented systems. Over 15 years experience installing cylinders in every type of South London property. We supply and fit leading brands including Megaflo, Telford, and Gledhill.
Thinking about switching to an unvented system? Here's why South London homeowners make the change
Unvented cylinders deliver water at mains pressure – typically 3 bar compared to 0.5 bar from gravity systems. This means powerful showers without pumps, baths that fill quickly, and strong flow from every tap. Multiple bathrooms can run simultaneously without pressure drop.
Traditional vented systems need a cold water tank in the loft, taking up space and requiring frost protection. Unvented cylinders connect directly to the mains, eliminating the loft tank completely. Reclaim that loft space for storage or conversion.
Water stored in open loft tanks can be contaminated by dust, insects, and debris. Unvented cylinders are sealed systems fed directly from the mains – cleaner, fresher water for drinking, cooking, and bathing.
Without gravity requirements, unvented cylinders can be installed almost anywhere – airing cupboards, utility rooms, garages, even ground floor locations. This flexibility suits South London properties where space is often limited.
Modern unvented cylinders have excellent insulation, reducing heat loss significantly compared to older vented cylinders. Less heat loss means lower energy bills and reduced carbon footprint.
Mains pressure hot water is a selling point for South London properties. Buyers expect powerful showers and modern plumbing. An unvented system adds genuine value when you sell.
Planning renewable energy? Unvented cylinders integrate with solar thermal panels and air source heat pumps. Future-proof your hot water system for greener heating options.
We focus on South London rather than spreading thin across the entire capital. All our engineers are based locally – when you book an installation in Bexley or Greenwich, we're already in the area. We've installed unvented systems in hundreds of South London properties.
Unvented cylinder installation requires specific G3 qualification – standard plumbers can't legally install these systems. All our engineers hold current G3 certification, ensuring your installation meets legal requirements and manufacturer specifications.
We're approved installers for Megaflo, Telford, and Gledhill – the UK's most trusted unvented cylinder brands. Approved status means proper training, access to technical support, and valid manufacturer warranties on installation.
Unvented cylinder installation requires Building Regulations notification. As Competent Persons Scheme members, we self-certify installations and handle all compliance documentation. No need for separate Building Control inspections.
We don't just fit cylinders – we design your complete hot water system. Correct sizing based on property needs, appropriate safety devices, optimal pipework configuration. Proper design means proper performance.
Cylinders come with manufacturer warranties up to 25 years. We guarantee our installation workmanship for 12 months. If any issues arise from our work, we return and fix them at no additional cost.
We'll tell you if an unvented cylinder isn't right for your property. Low mains pressure, inadequate incoming supply, or property limitations may mean alternatives are better. Honest advice, not just sales.
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We supply and install all leading unvented cylinder brands found in South London properties
Megaflo by Heatrae Sadia is the UK's best-known unvented cylinder brand. Industry-leading reliability with warranties up to 25 years. Excellent build quality, comprehensive safety systems, and widely available parts. Our most recommended brand for South London installations.
Standard in South London flats and houses. We test burner operation and flame picture, check gas tightness at connections, verify stability (cooker won't tip), test operating pressure, and confirm ventilation requirements are met.
Common in South London period properties across Greenwich and Blackheath. We check flame picture and combustion, test flue integrity, verify ventilation adequacy, confirm safety controls operation, and assess visual condition.
All visible gas pipework is inspected for corrosion or damage, adequate support and fixing, accessible emergency control valve, and meter condition and location.
Critical safety checks including flue terminal obstruction check, spillage tests for escaping combustion products, ventilation grille adequacy, and room sealed appliance verification. Common issues in South London's Victorian and Edwardian conversions – inadequate ventilation in converted rooms.
All safety features tested including flame failure devices (cut gas if flame extinguishes), thermostats and overheat protection, pressure relief valves, and interlock systems.
Don't worry – our engineers can identify and repair any boiler. Call us for expert diagnosis and repair.
What actually happens when you call for emergency boiler repair—from first contact to 12-month guarantee.
We visit your South London property to assess suitability. We check mains water pressure and flow rate, identify optimal cylinder location, and discuss your hot water requirements. This survey is free and without obligation.
We reach out to arrange convenient access. We work around tenant schedules – evenings and weekends available. Professional, courteous approach – we represent you well to your South London tenants.
You receive a comprehensive written quote covering all work, materials, and timescales. The price is fixed – no surprises during installation. We explain everything and answer questions before you commit.
Once you approve the quote, we schedule installation at a time that suits you. Most unvented installations take 1-2 days depending on complexity. We confirm dates and explain what to expect.
If replacing an existing cylinder or converting from a vented system, we remove old equipment safely. Loft tanks are drained and removed. Old pipework is capped or removed as appropriate.
Your new cylinder is installed in the agreed location. All pipework, safety devices, and controls are fitted. We work cleanly, protecting your property throughout installation.
We issue Building Regulations compliance certificates under Competent Person Schemes. This is lodged with your local council automatically. You receive documentation for your records.
We commission the system, test all safety devices, and verify correct operation. You receive full demonstration of controls and maintenance requirements. All documentation including warranty cards is provided.
We believe in transparent pricing for all certificates. Our rates are based on two service zonesUnvented cylinder costs vary based on size, brand, and installation complexity:
Several factors influence unvented cylinder installation pricing
Adequate mains pressure (minimum 1.5 bar, ideally 3+ bar) and flow rate (minimum 20 litres/minute) are essential. If your supply is marginal, we may need to install accumulator tanks or recommend alternatives. Very high pressure requires pressure reducing valves.
Larger properties with multiple bathrooms need bigger cylinders. A 4-bed house with 2 bathrooms needs 250+ litres, while a 2-bed flat might only need 150 litres. Bigger cylinders cost more and need more space.
Easy access locations keep costs standard. Tight airing cupboards, basement installations, or locations requiring significant pipework runs add time and materials. Cylinder location affects installation complexity.
Converting from a vented system (with loft tank) involves more work than replacing an existing unvented cylinder. Loft tank removal, pipework modifications, and additional safety devices add to the cost.
Premium brands like Megaflo and OSO cost more than budget options. Stainless steel cylinders cost more than copper. Solar-ready cylinders with dual coils cost more than standard single-coil units. We explain options so you can choose.
South London's diverse properties each suit different unvented cylinder configurations:
Period properties common across Greenwich, Blackheath, Dulwich, and Forest Hill often have high ceilings and spacious airing cupboards perfect for unvented cylinders. Converting from old gravity systems dramatically improves shower pressure. Conservation area restrictions rarely affect internal cylinder installation.
Predominant across Bexley, Bromley, and Streatham. These properties typically have good-sized airing cupboards and adequate mains pressure. Ideal candidates for unvented conversion. Loft tank removal creates useful storage space.
Flats suit compact unvented cylinders – 120-170 litre units fit most airing cupboards. Mains pressure is usually good in flats. Slimline and horizontal options work where standard cylinders won't fit. Check lease for any installation restrictions.
Greenwich Peninsula, Woolwich Arsenal, and Canada Water properties often have unvented cylinders already. If replacement is needed, we match specifications and maintain any building warranties. Good mains infrastructure supports larger cylinders.
Properties with 3+ bathrooms need correctly sized cylinders – typically 250-300 litres. Mains flow rate becomes critical with multiple simultaneous users. We calculate requirements carefully to ensure adequate supply.
Unvented cylinders need adequate mains water pressure and flow. Here's what we check:
We measure actual pressure and flow during the survey – not estimates. If your supply is marginal, we'll discuss options: accumulator tanks to boost supply, or recommend combi boiler alternatives. We won't install systems that won't perform properly.
Thames Water's hard water (250-320mg/l) affects unvented cylinders over time. We recommend scale reducers for South London installations to protect your investment and maintain performance.
Unvented cylinder installation legally requires G3 qualification. This certification covers the specific safety requirements of pressurised hot water systems. Standard plumbing qualifications aren't sufficient. All HeatBox engineers installing unvented systems hold current G3 certification.
Unvented installations must comply with Building Regulations. Part G covers hot water safety, Part L covers energy efficiency. As Competent Persons Scheme members, we self-certify compliance and lodge notifications automatically.
Unvented cylinders require multiple safety devices: expansion vessel (accommodates water expansion), temperature and pressure relief valve (prevents dangerous pressure buildup), tundish (visible discharge indicator), and expansion relief valve. All must be correctly specified and installed.
If safety valves activate, hot water must discharge safely. Building Regulations specify pipe sizes, materials, and termination points. Discharge must be visible (via tundish) so problems are noticed. We design compliant discharge routes for your property.
All our engineers are Gas Safe registered with £5M public liability insurance. We comply with all Building Regulations, provide landlord certificates, and maintain complete legal compliance for every job across London.
HeatBox provides unvented cylinder services with specialist focus on South and South East London:
South & South East London Specialists
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Not sure if you have an emergency? Call us and we'll help you assess urgency and prioritise accordingly across our London coverage areas.
Clear access to the installation location – typically an airing cupboard or utility area. If we're removing a loft tank, ensure loft access is clear. Note any stored items that need moving. We'll advise specific preparation after the survey.
Installation typically takes 1-2 days. Day one usually involves removal of old equipment and preparation. Day two completes installation, commissioning, and testing. You'll be without hot water during installation – we'll advise on timing to minimise inconvenience.
Your system is ready to use immediately after commissioning. Enjoy mains pressure hot water throughout your property. We demonstrate controls and explain maintenance requirements. All documentation is provided for your records.
Book annual servicing to maintain warranty and safety. Don't ignore discharge from safety valves – this indicates problems needing attention. Report any pressure loss, unusual noises, or performance changes promptly. With proper maintenance, your cylinder will last decades.
Customers who installed unvented cylinders also used
Unvented cylinders pair with system boilers or regular boilers. We install complete heating systems optimised for your new cylinder.
Annual boiler servicing keeps your heating system running efficiently alongside your unvented cylinder. From £90..
Complete heating system installation including unvented hot water. Ideal for properties needing full upgrades.
Clean your heating system before or after cylinder installation for optimal performance. £500 Zone 1.
Planning underfloor heating? We design integrated systems with unvented hot water.
Over 15 years serving London with transparent pricing, specialist knowledge, and genuine emergency response. No corporate markup, just honest local service.
Unvented cylinder installation typically costs £1,500-£3,500 depending on cylinder size and installation complexity. Small cylinders (120-150L) for flats start around £1,500. Large cylinders (250-300L) for family homes cost £2,800-£3,500. We provide fixed quotes after free surveys.
Megaflo offers the best combination of reliability, warranty (up to 25 years), and parts availability. Telford and Gledhill are excellent alternatives. We recommend based on your specific requirements and budget.
Yes – if you're experiencing hot water limitations from a combi boiler, switching to a system boiler with unvented cylinder provides unlimited hot water at mains pressure. We assess whether this upgrade suits your property.
Ready for powerful showers and fast-filling baths? Book your free survey and get a fixed price quote for unvented cylinder installation.
Serving Bexley, Greenwich, Lewisham, Bromley, Croydon & All South London
G3 Qualified | Approved Installers | Mains Pressure Specialists
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