Hot Water Cylinders
Across London — G3
Qualified, Compliant.
Unvented and vented hot water cylinders installed, replaced, serviced and repaired across London. Megaflo, OSO, Gledhill, Telford and Range — sized for your household demand, installed to G3 Building Regulations, and signed off with a written commissioning report your buildings insurer expects to see.
Cylinder work done by a G3-qualified engineer.
An unvented hot water cylinder is a pressurised vessel storing hot water at mains pressure. Under Building Regulations G3, installation and non-routine work on an unvented cylinder can only be legally carried out by a G3-qualified engineer — and every buildings insurer treats work done without G3 as grounds to void a claim. Chelsea Plumbing & Heating Co. is G3-qualified; every unvented install and repair we carry out is compliant, notifiable and insurance-safe.
We install, replace, service and repair unvented and vented hot water cylinders across London — direct and indirect, twin-coil solar-ready, high-recovery cylinders for heavy hot-water use, and commercial booster-fed systems for houses with mains pressure or flow limitations.
Suits homeowners upgrading from an old vented cylinder or a tired combi to full unvented mains-pressure hot water, refurb clients scoping a new bathroom or extension that increases hot-water demand, landlords whose existing cylinder is failing under duty, and anyone with an existing unvented cylinder that hasn't been serviced (an annual service on the safety devices is required — most homeowners don't know this).
Owner-led by Ian Fisher directly — Gas Safe registered (952303), G3-qualified, and many years in the trade. Same engineer specifies it, installs it, commissions it and services it.
The reasons an unvented install goes wrong.
The most common problem is discharge pipework. The tundish, D1 discharge and D2 discharge on an unvented cylinder are specified in Building Regulations G3 — diameters, distances, terminations. Cylinders installed by anyone without G3 frequently discharge into inadequate pipework or to a non-compliant termination, and on the day the pressure-reducing valve fails the discharge cannot cope. Water goes somewhere it shouldn't.
The second is expansion. An unvented cylinder needs an expansion vessel sized for the cylinder capacity, pre-charged to the correct pressure, and re-charged periodically (annually on service). Skip the pre-charge and the pressure-relief valve weeps constantly, the vessel corrodes internally, and eventually the whole cylinder scraps.
The third is annual service. Unvented cylinders have three safety devices — expansion relief valve, temperature relief valve, and the immersion cut-out — and Building Regulations G3 requires them to be inspected and tested annually. Most homeowners never have this done. When one of the safety devices fails, the cylinder discharges under pressure and the resulting damage is uninsured.
- ×Unvented cylinder installed by a non-G3-qualified plumber — Building Regulations breach and insurance-voiding.
- ×Undersized D2 discharge pipework to a non-compliant termination — cannot cope when the safety devices operate.
- ×Expansion vessel pre-charge never re-checked — pressure-relief valve weeps and the cylinder is scrapped early.
- ×Cylinder sized on the old vented capacity, not on current household demand — runs out during morning showers.
- ×Skipping the annual service on an existing unvented cylinder — safety devices drift and no one knows until they fail.
- ×Immersion heater fitted without the correct thermal cut-out replaced — the primary safety device against a boil-dry event is missing.
A methodical system,
not a rushed callout.
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01SurveyHousehold hot-water demand assessed (bathrooms, shower type, occupancy), mains pressure and flow tested, existing cylinder inspected.
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02SpecifyCylinder brand, capacity, coil arrangement (direct, indirect, twin-coil), expansion vessel and pipework upgrades quoted in writing.
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03InstallOld cylinder isolated and removed, new cylinder positioned, indirect coil piped to the boiler primary, expansion vessel and G3 discharge pipework installed to spec.
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04CommissionPressure-reducing valve set, expansion vessel pre-charged, safety devices tested, cylinder heated to full temperature and hot-water outlets flow-tested.
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05Sign-offBuilding Regulations notification submitted, written commissioning certificate issued, benchmark logbook completed, 12-month workmanship guarantee in writing.
Concrete outcomes,
not vague promises.
G3 qualified and compliant
Legally qualified for unvented cylinder installation and repair — the qualification your buildings insurer wants to see and Building Regulations require.
Sized to actual household demand
Not just replacing the old capacity — sized on current bathrooms, shower type, occupancy and mains flow, so you don't run out mid-morning.
Building Regulations notification
New unvented installs are Building Regulations notifiable — we submit the notification and issue you the certificate for your property records.
Twin-coil solar and heat-pump ready
Where required, twin-coil cylinders installed for solar-thermal integration or air-source heat pump compatibility on the primary coil.
Annual service programme
Existing unvented cylinders serviced annually as G3 requires — expansion vessel re-pressurised, safety devices tested, immersion element inspected.
Written commissioning certificate
Every install and every service comes with a written report — for your records, for your insurer, and for the next owner if you ever sell.
Photographs from
actual jobs.
Real installations, repairs and diagnostics carried out by Ian across London and the Home Counties. No stock photography.
Cylinder work we cover.
Everything below is carried out by a G3-qualified, Gas Safe registered engineer — installation, servicing and repair of both unvented and vented systems.
Unvented cylinder installation
Megaflo, OSO, Gledhill Stainless Lite, Telford Tempest and Range Tribune installed. Direct (electric-only) or indirect (boiler-fed). Correct expansion vessel, PRV, tundish and G3 discharge pipework as standard.
Vented cylinder installation
Copper and stainless steel vented indirect cylinders installed where the property or client preference requires — including full pipework to the header tank and cold-feed configuration.
Cylinder replacement (like-for-like)
Existing cylinder isolated, drained, disconnected and removed. New cylinder positioned, piped and commissioned. Old cylinder taken away.
Immersion heater replacement
Immersion element replacement including thermal cut-out where fitted — sized to the cylinder and re-commissioned against manufacturer spec.
Expansion vessel replacement & re-charge
Annual expansion vessel pressure check as G3 requires. Vessel replacement where the pre-charge cannot be restored or the bladder has failed.
Pressure-reducing valve (PRV) service
PRV inspection, set-pressure verification and replacement where the outlet pressure has drifted beyond spec (common cause of PRV weep and cylinder discharge).
Tundish and discharge (D1/D2) pipework
G3-compliant tundish, D1 vertical run and D2 termination installed and tested — the safety layer against pressure-relief operation on a failed cylinder.
Twin-coil solar & heat-pump cylinders
Twin-coil cylinders for solar-thermal panel integration or air-source heat pump compatibility installed and commissioned to the manufacturer's schematic.
Annual cylinder service
Full G3-compliant service — expansion vessel re-charged, PRV and TPRV tested, immersion tested, tundish and discharge inspected, written report issued.
Is a G3 qualification really a legal requirement?
Yes — under Building Regulations G3, installation and non-routine work on an unvented hot water cylinder must be carried out by a G3-qualified competent person. Non-compliant work is a Building Regulations breach and every mainstream buildings insurer treats it as grounds to void a claim.
How much does an unvented cylinder installation cost in London?
A like-for-like unvented replacement is typically £2,200–£3,500 fitted depending on cylinder capacity, brand and pipework upgrades. New installs where old vented pipework needs re-plumbing are priced per job in writing.
How big a cylinder do I need?
For a typical London home, a 3-bed with one bathroom is usually 150–180 litres; two bathrooms 210–250 litres; a family home with multiple showers 250–300+ litres. We size on actual household demand, not just the old cylinder's capacity.
How often should an unvented cylinder be serviced?
Annually. Building Regulations G3 requires the safety devices to be tested and the expansion vessel pre-charge re-verified once a year. Most manufacturer warranties are conditional on an annual service.
How long does an unvented cylinder installation take?
A like-for-like unvented swap is typically a single day. Full new installs with pipework upgrades and Building Regulations sign-off can run to 1–2 days depending on complexity.
Do you install twin-coil cylinders for solar or heat pump?
Yes — twin-coil unvented cylinders for solar-thermal panel integration and air-source heat pump compatibility are installed and commissioned to the manufacturer's schematic.
Can you repair an existing unvented cylinder?
Yes — PRV service, expansion vessel re-charge and replacement, immersion replacement and safety device testing all carried out by a G3-qualified engineer.
Do I get Building Regulations sign-off paperwork?
Yes — every new unvented install is notified under Building Regulations G3 and you receive the certificate for your property records. Essential for any future sale.
What guarantee do I get?
12-month workmanship guarantee in writing on the install. The cylinder itself carries the manufacturer warranty on top (typically 25 years on the vessel for Megaflo, OSO and Gledhill quality brands).
Which areas do you cover?
Greater London and the surrounding Home Counties — Kent, Surrey, Essex, Hertfordshire, Buckinghamshire, Berkshire, Bedfordshire, Middlesex and West Sussex.
Fixed price. Gas Safe.
12-month guarantee.
Free estimates from Ian directly — no call centre, no subcontractors, no surprise bills. One point of contact from first call to twelve-month follow-up.