07956 994429 020 8244 0912 INFO@DHPLUMBING.CO.UK GAS SAFE REGISTERED#180521 AboutServices Service Areas Our WorkReviewsContact 07956 994429020 8244 0912 Request EstimateQuote - Home - Services - Unvented Cylinders (G3) Gas Safe #1805214.9★ · 159 Google reviews30+ years local # Unvented Cylinder Installation (G3)in Woolwich & Greenwich Mains-Pressure Hot Water, Installed Safely Mains-pressure hot water to every tap in the house: Megaflo, Telford and Heatrae Sadia unvented cylinders supplied, installed, serviced and safety-inspected by a G3-qualified engineer with over 30 years on SE London homes. Request a free estimate Call 07956 994429 Call 020 8244 0912 G3 qualified engineer · Full annual service · Building Control notification handled 30+ yrs Local experience 180521 Gas Safe registered 4.9★ 159 Google reviews £5m Public liability insured 9–9 Office, 7 days a week Overview ## High-pressure hot water, done safely An unvented cylinder is a pressure vessel. It has to be installed and maintained by someone qualified to do it: G3 exists for a reason. What it isInstallation, servicing and safety inspection of unvented hot water cylinders, direct or indirect, coil-fed by a system boiler or immersion-heated. Includes discharge pipework, pressure and temperature relief, expansion vessel and full commissioning. Who it's forHomes and flats in SE London with two or more bathrooms, or one bathroom plus high hot-water demand, moving away from a gravity or combi setup. Also landlords running HMOs where multiple bathrooms need independent flow. When you need itWhen your current hot water arrangement can't keep up with demand, on a full central heating replacement, on a new bathroom or ensuite addition, or on the annual G3 safety inspection. Why a professional mattersUnvented cylinders are Building Regulations G3 notifiable, installation, servicing and safety must be carried out by a qualified engineer. Poorly installed cylinders have caused fatalities from over-pressurisation. What’s at stake ## Why unvented cylinders are the one appliance you don't cut corners on The worst outcomes in domestic plumbing come from unvented cylinders installed or serviced by people who weren't qualified to. ### Discharge pipe wrongly routed Discharge from the T&P relief valve must run to a safe external termination, routing internally can steam-scald anyone nearby if the valve blows. ### Expansion vessel loss A tired expansion vessel means the T&P valve blows on every heat-up. Left unchecked, the safety valve itself will fail. ### Overpressurisation risk A cylinder without functional safety devices can become a pressure vessel with steam-explosion energy, historically responsible for UK domestic fatalities. ### Failed Building Control An unregistered installation is unlawful under Approved Doc G3, buyers' solicitors flag it, and it must be remedied before sale. Common mistakes we fix - Trusting a general plumber without G3 certification - Skipping the annual service, mandatory for safety - Not testing expansion vessel pressure annually - Wrongly routed discharge pipework - Missing Building Control notification Our process ## From your first call to the completion certificate. - 1 ### Survey Cold mains flow tested, cylinder location planned, discharge route confirmed, coil compatibility with boiler assessed. - 2 ### Design & spec Cylinder size (150L, 210L, 300L etc), direct or indirect, coil kW rating and controls specified and quoted in writing. - 3 ### Installation Cylinder positioned, all safety devices fitted (T&P, expansion, PRV), discharge pipework routed correctly, coil connected to boiler. - 4 ### Commissioning System filled, air purged, expansion vessel pre-charged to correct pressure, T&P tested, temperature control confirmed. - 5 ### Certification Building Control notified, G3 certificate issued, manufacturer warranty registered, annual service reminder set. Benefits ## What you actually get for the money. ### Full mains pressure at every tap Multiple showers running simultaneously with no drop in flow. ### No loft tank required Frees loft space, eliminates freeze and legionella risks. ### Compatible with power showers Direct mains pressure supports power showers and body-jet systems. ### Fast recovery Large indirect coils re-heat 210L in 25–35 minutes on a modern system boiler. ### Long service life Correctly installed and annually serviced, 15–20 years is entirely normal. ### Safe by design G3-qualified installation and annual servicing keep all safety devices functional. Technical detail ## What a G3-compliant unvented installation involves G3 is a rigorous qualification, and the standards attached to it are the reason unvented cylinders are safe. ### Sizing the cylinder 150L for a two-person flat, 180–210L for a family home with 2 bathrooms, 250–300L for larger houses or high-demand HMOs. Undersized cylinders are the top cause of complaint six months post-install. ### Direct vs indirect Indirect (heated by boiler coil) is the norm for gas-heated homes; direct (electric immersion only) suits off-gas properties or as a backup. Twin-coil versions accept solar thermal or heat pump input. ### Safety devices Temperature and pressure relief valve, pressure relief valve, expansion vessel, tundish and discharge pipework, every one required, tested at commissioning and re-tested annually. ### Discharge pipework routing Discharge from the T&P valve runs to an external safe termination via correctly-sized tundish and D1/D2 pipework, complying with Approved Doc G3. This is where the majority of failed inspections happen. ### Manufacturers we install Megaflo (Heatrae Sadia), the SE London default; Telford Tempest and Hurricane, good performance and parts availability; Gledhill Stainless Lite for compact installations. ### Annual service and G3 inspection Expansion vessel pressure test, T&P valve test, safety device inspection, coil pressure check, discharge route re-inspection, and full written report, mandatory annually to keep safety and warranty valid. Recent work ## Photos from real jobs, not stock imagery. See the full gallery → Frequently asked ## Questions we hear every week. What is a G3 qualification?+G3 is the specific Building Regulations qualification required to install, service and safety-inspect unvented hot water cylinders in the UK. Only G3-qualified engineers can legally do this work. How much does an unvented cylinder installation cost?+£2,200–£3,200 for a 210L indirect Megaflo in a typical SE London home, including safety pack, expansion vessel, tundish and discharge pipework. Larger or twin-coil cylinders £2,800–£4,000. How long does the installation take?+1–2 working days for a straightforward replacement. 2–3 days where relocating or converting from a vented system. How often should an unvented cylinder be serviced?+Annually, this is not optional. Expansion vessel loses pressure over time; safety devices need testing; discharge route must be re-inspected. How much does the annual G3 service cost?+£95 for a standard indirect cylinder, including full safety device testing, expansion vessel pressure check and written report. What size cylinder do I need?+180–210L for a typical 3-bed family home with 2 bathrooms; 250–300L for larger households or HMOs. We'll size on your usage pattern. Do you handle Building Control notification?+Yes, G3 notifiable installs are registered through our competent-person scheme at no extra cost. You receive the compliance certificate. What happens if the safety valve blows?+It means the expansion vessel or PRV has failed and needs immediate attention, call us and we'll come out as a priority. Do not ignore a valve that has discharged. Book unvented cylinders ## Ready to get unvented cylinders sorted properly? Speak to Danny directly. Free quote in writing, honest advice, and a fair fixed price. No sales pressure, we’ve been at this for over 30 years for a reason. Call 07956 994429 Call 020 8244 0912Request estimate - Gas Safe registered #180521 - 4.9★ from 159 Google reviews - Office 8am–9pm, 7 days a week - Based in Greenwich · covers all SE London Related services ## Often booked together. See all services → Service ### Boiler Installation Learn more Service ### Central Heating Installation Learn more Service ### Bathroom Installation Learn more Service ### Heating Engineer Learn more Gas Safe registered plumbing, gas & heating engineers with 40 years of local experience across South East London. Gas Safe #180521 Company No. 06064438 Services - Boiler Installation - Boiler Repairs - Power Flushing - Gas Safety Engineer - Landlord Gas Safety (CP12) - Gas Fires & Cookers - Heating Engineer - Central Heating Installation Service Areas - Greenwich · Woolwich - Blackheath · Eltham - Thamesmead · Plumstead - Abbey Wood · Erith - Dartford · Bexley · Sidcup Contact - 07956 99442924/7 Emergency - 020 8244 0912Office landline - info@dhplumbing.co.uk - London - Office: 8am – 9pm, 7 days a week © 2026 DHP London Ltd. All rights reserved. AboutOur WorkReviewsContactPrivacyTerms Call nowGet a quote