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Hot Water Cylinder Replacement in London

£1,450 fixed for labour and miscellaneous parts to replace a cylinder, with the cylinder itself shown as its own line on a written quote. A new installation is £2,400. A diagnosis to decide repair or replace is £180.

Prices checked 27 October 2026. We do not currently charge VAT, so these are the totals for labour and parts. Pre-booked cylinder work has no call-out fee; same-day and out-of-hours emergency call-outs are £60 at any hour.

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25yr Manufacturer tank warranty
12mo Workmanship guarantee
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Quick answer

Replacing a hot water cylinder in London costs £1,450 for our labour and parts, plus the cylinder, which is priced as a separate line. A first-time installation or conversion is £2,400 plus the cylinder. Many cylinder faults do not need a new tank: in our own cylinder jobs between August and October 2026, four of sixteen were replacements.

Hot water cylinder replacement cost in London

These are the prices we quote. Labour and parts are fixed; the cylinder is a separate line because the make, size and type change the total more than anything else, and a separate line lets you compare our quote with any other.

JobFixed priceWhat it covers
Cylinder fault diagnosis£180Engineer attends, tests the cylinder, controls and safety devices, and gives a written repair-or-replace recommendation with a fixed price for each.
Cylinder replacement (labour and miscellaneous parts)£1,450Like-for-like swap: drain down, remove the old cylinder, fit the new one, reconnect, commission. The cylinder itself is a separate line on your quote.
New cylinder installation£2,400Pipework, installation, commissioning and Building Regulations work for a first-time installation or a conversion. The cylinder is a separate line on your quote.
Hot water cylinder service (annual unvented service)£180The yearly safety and pressure checks manufacturers ask for to keep a warranty valid, with the logbook updated.

Prices checked 27 October 2026. No VAT is currently added to any of these prices. The cylinder is quoted separately on every job. Repairs to valves, thermostats and elements are priced on the hot water repair page and confirmed in writing before work starts.

How that compares with published guides

JobRange quotedSource and basis
Like-for-like unvented replacementabout £2,245 to £2,369Hamuch, London estimate pages, excluding VAT and call-out
Unvented replacement, UK-wide, all-in£2,000 to £3,800BookaBuilderUK, with London at the top of the range

Third-party ranges as published in October 2026. They are not our prices and mix cylinder, labour and extras differently, which is why we show ours split out.

What moves the price

  • Vented to unvented. Adds work: new mains feed, discharge route to outside, expansion vessel, loft tank removed. This is the £2,400 job, not the £1,450 one.
  • Discharge route. The hardest part in mid-floor flats. A long or awkward run to an outside wall costs more time than the cylinder swap itself.
  • Access. Loft hatches, tight airing cupboards and top-floor flats with no lift change how long carrying and fitting takes.
  • Which cylinder. Size, brand and whether it is direct, indirect or smart. This is its own line on the quote, so you can compare it with any other quote.
  • Old pipework. Corroded valves or isolators that will not shut off cost extra to replace. We find these at the survey, not on the day.

Not sure which price applies? A diagnosis tells you in writing.

Call 0207 046 1363

Hot water cylinder repair or replacement: what decides it

From August to October 2026 we logged 16 completed cylinder-related jobs. Four were replacements. The rest were diagnostics, valve and element repairs, a recommissioning visit, annual services and leak work. It is a small sample, but it matches the usual pattern: most cylinder complaints are a part, not the tank. From our earlier work, a failed expansion vessel typically costs £180 to £280 to replace, a temperature and pressure valve £120 to £160 and an immersion element £90 to £130, all of them far less than a new cylinder.

What you seeIt usually isRepair or replace
Water dripping from the tundish only while the water is heatingExpansion vessel or its pressure has failedRepairCylinder is usually fine. Leave the discharge pipe open.
Tundish running constantly, hot or coldPressure reducing valve or inlet group faultyRepairValve replacement is a common job; the tank is not the fault.
Leak from a relief valve or combination valveValve has failed or is not reseatingRepairOn one August job we replaced both the temperature-and-pressure valve and the combination valve. The cylinder stayed.
No hot water but the heating worksMotorised valve, cylinder thermostat or immersion elementRepairFault-find before anyone suggests a new cylinder.
Both immersion elements dead on an electric cylinderScale and ageRepair, if the tank is soundIn October we replaced top and bottom elements on one cylinder. It is a repair as long as the shell is dry.
Water weeping from the shell, seams or baseThe tank itself has failedReplaceA failed shell cannot be repaired.
Brown water from the hot tap only, or visible corrosionCorroding cylinder or coilReplaceConfirm it is the cylinder, not the pipework, before booking.
Second or third component failing in a year on an old unitEnd of lifeReplaceRepair money starts to go into a tank that will not last.
Vented cylinder with a weak shower and a loft tankLow head of water, not a faultReplace with unventedOnly worth it if mains pressure and a discharge route allow.
Stop and call an engineer: steam or scalding water from the tundish, water coming through a ceiling, or a burning smell at the immersion. Switch off the heat source and the electric supply to the immersion, keep clear and do not block the discharge pipe. Unvented cylinders are engineer-only work.

Not sure if yours is a repair? We diagnose first for a fixed £180.

Get a fixed price

Recent cylinder jobs, in photos

Photos from our own cylinder jobs this autumn. Several show a repair that saved the customer a new cylinder.

A new 50 litre cylinder with its expansion vessel and valve group fitted above a kitchen worktop
A 50 litre cylinder swap: new cylinder, expansion vessel and valve group.
A Megaflo direct hot water cylinder in an airing cupboard after its immersion elements were replaced
A Megaflo direct cylinder after both immersion elements were replaced. No new tank needed.
Old immersion elements removed from a hot water cylinder lying on the floor beside tools
Old elements out of a cylinder. A worn element is a repair, not a replacement.
A brass combination valve and relief valve group on a cylinder being replaced by an engineer in orange gloves
The valve group replaced on a leaking cylinder. The cylinder stayed.
An expansion vessel and red-topped relief valve beside an unvented cylinder
Expansion vessel and relief valve beside an unvented cylinder.
Two grey expansion vessels held side by side during a swap on an unvented cylinder
Two expansion vessels side by side during a swap, the usual cause of a tundish drip.

Which type of cylinder do you have, and which should you fit?

The two decisions that change the job most are vented or unvented, and direct or indirect. If you are unsure what you have, the answer is on the cylinder: a loft tank means vented, a tundish and expansion vessel mean unvented.

  • Unvented (sealed, mains pressure)

    No loft tank. It is fed straight from the mains, so showers run at mains pressure. Fitting and servicing is notifiable work under Part G of the Building Regulations, so it needs a G3 qualified engineer. You can spot one by the tundish (a small funnel on the discharge pipe) and the expansion vessel.

  • Vented (open vent, loft tank)

    Fed from a cold-water tank in the loft, so pressure depends on the height of the tank above the cylinder. Common in older London homes. If the loft tank and a vent pipe are there, it is vented. Often the cheapest like-for-like swap where the tank is staying.

  • Direct (immersion heated)

    Heated by one or two electric elements only, with no boiler coil. Found in all-electric flats and homes off the gas network. Two elements fail separately, which is why a half-hot cylinder is often an element, not a tank, problem.

  • Indirect (boiler heated)

    A coil inside the cylinder carries heat from the boiler. The usual set-up behind a gas system boiler, normally with a backup immersion element as well.

  • Smart cylinders (for example Mixergy)

    Heat only the top part of the tank and can be controlled by an app or tariff. They make most sense with solar PV, cheap-rate electricity or a heat pump on the way.

Moving from vented to unvented is worth it when the mains has enough pressure and flow and there is a route for the discharge pipe to reach outside. If either is missing, a vented swap is the honest answer. Manufacturers publish the minimum mains pressure and flow for each model, so we measure before we recommend.

What size cylinder do you need?

A common rule of thumb is 35 to 45 litres per person, with extra for a second bathroom or a daily bath. Use the table as a starting point and read the full sizing guide if two showers run at once.

PropertyPeopleBathroomsStarting size
Studio or 1-bed flat11 showerabout 120L
2-bed flat or maisonette2 to 31 bath or showerabout 150 to 170L
3-bed terrace or semi3 to 41 bath and 1 showerabout 180 to 210L
4-bed family home4 to 52 bathroomsabout 210 to 250L
5-bed or larger5+2 to 3 bathroomsabout 250 to 300L

Four checks that decide whether a cylinder suits your property

These are the points that turn a straightforward quote into a surprise on the day. Each one comes from a manufacturer manual or an official source, linked so you can read the original.

Mains pressure and flow

The water supplier's guaranteed standard is low, about 0.7 bar (7 m head), with about 1 bar as its aim. Heatrae Sadia's Megaflo Eco installation manual asks for a minimum of 1.5 bar and 20 litres a minute at the cylinder. A house can meet the first and miss the second, so measure dynamic pressure with water running and time a bucket fill rather than trusting a static gauge reading.

WaterSafe: minimum water pressure

Where the discharge pipe can go

Approved Document G sets out the discharge rules: the tundish within 600 mm of the safety valve, set vertically with a visible air gap, then a pipe that drops at least 300 mm and falls at 1 in 200, sized up once the run is longer than 9 m equivalent. In a mid-floor flat with no outside wall nearby, this is the check that decides whether an unvented cylinder is possible at all.

GOV.UK: Approved Document G

Will it fit, and will the floor carry it

Measure the external size including the insulation, not the tank volume, and check the loft hatch, stairs and door widths. A 210-litre Megaflo weighs about 250 kg when full according to its manual, which matters for an upper floor or a boarded loft.

Megaflo Eco installation manual (Heatrae Sadia)

Hard water and your warranty

The Drinking Water Inspectorate calls water of 200 to 300 mg/l hard and anything over 300 mg/l very hard, and most of London sits in those bands. Some manufacturers exclude scale damage, and Joule's instructions set a hardness limit of 200 mg/l for its warranty, so check what scale protection your maker expects before you rely on the warranty.

Drinking Water Inspectorate: water hardness

What the manufacturer warranty actually says

Warranty length varies by maker and model, and every one depends on the cylinder being registered on time and serviced each year. Terms below are from the makers' own published pages and manuals; they change, so check the current wording for the exact model you are quoted.

MakerCoverConditions in the small print
Heatrae Sadia Megaflo EcoLifetime for the first domestic owner, 30 years on resaleAnnual service, registration within 30 days, scale and frost excluded
TelfordLifetimeRegistration within 28 days, Benchmark checklist and service record needed for a claim
Joule25 years on the vesselRegistration within 28 days, annual service log, scale and labour excluded, water chemistry limits

Sources: Heatrae Sadia product warranty page, Telford and Joule installation instructions, read October 2026. A missing service record is the most common reason a claim fails.

What happens from first call to finished job

1

Phone or WhatsApp

Call 0207 046 1363 or message 07456 975436. We ask the cylinder type, rough age and what has gone wrong, and give you the fixed prices above.

2

Diagnosis or survey

The engineer checks mains pressure and flow, the cupboard, the discharge route and the condition of the pipework, then tells you in writing whether to repair or replace.

3

Written quote

Labour and parts, the cylinder and any extras each on their own line. You see what is included before anything is ordered.

4

Fitting day

A like-for-like unvented swap is typically half a day to a day, and hot water is back the same day on about 95% of our jobs. A vented-to-unvented conversion takes longer because the mains feed, discharge route and expansion vessel are all new.

5

Commissioning and paperwork

Pressure and temperature devices are tested, the logbook is completed and the Building Regulations notification is made. Ask for the certificate and keep it with the house papers.

G3 qualified plumber: unvented cylinder installation and Building Regulations

Any unvented cylinder over 15 litres is covered by Part G of the Building Regulations (Approved Document G). Installing, replacing or modifying one is notifiable work, so the installer must be G3 qualified and either belong to a competent person scheme or notify Building Control. In practice that means three things to ask for:

  1. Proof the engineer is G3 qualified before any drain-down starts.
  2. The Building Regulations certificate once the work is notified. Keep it with your buildings insurance and conveyancing papers.
  3. A completed logbook from commissioning. Manufacturers usually ask for annual servicing to keep a warranty valid, so check the terms for your model.

Our engineers are G3 qualified. See the G3 explainer and how to check an engineer before you book anyone.

Past London cylinder jobs

Five anonymised jobs completed by our engineers over previous years, before they joined Emergency Repairs London. Prices are what was charged at the time and are not today's quote, so use the fixed prices above for a current figure. They show how much the discharge route, access and cylinder type drive the cost.

Victorian conversion, Camden: vented to 210L Megaflo Eco

1890s terrace, top-floor flat, original loft tank feeding a 1985 copper indirect cylinder, dribbling shower. Mains tested at 3.4 bar dynamic. Loft tank removed, 210L Megaflo Eco fitted in the airing cupboard, discharge piped through the soffit and G3 notification made. Job time: 9 hours. Total: £2,395.

1930s semi, Hackney: like-for-like 180L Telford swap

Twelve-year-old Range Tribune HE 180L. The expansion vessel had failed twice in twelve months and the tank was starting to weep at the lower boss. Replaced with a Telford Tempest 180L, new G3 safety group, same discharge route, primary coil reconnected. Six hours, £1,745.

Apartment block, Wandsworth: 150L Megaflo direct

All-electric Battersea apartment block, original 2008 150L direct cylinder, both elements scaled solid and the tank lining starting to bubble. New 150L Megaflo direct fitted with two new immersions on Economy 7 wiring. £1,495.

Georgian townhouse, Westminster: 300L OSO Super S

Four-bath property on an original 1990s vented system where two showers could not run at once. Full vented-to-unvented conversion, 300L OSO Super S stainless cylinder in the basement plant room, mains upgraded to 28mm, discharge to a gully under the stairs. Two-day install. £3,295.

Heat-pump-ready upgrade, Islington: Mixergy 210L

Homeowner planning an air-source heat pump. Existing 1995 vented cylinder replaced with a Mixergy 210L heat-pump-ready smart cylinder, installed with a PV diverter and an agile tariff. £3,495.

Questions to ask any firm before you accept a quote

Cylinder quotes are hard to compare because they bundle different things. These eight questions work on ours and on anyone else's:

  1. Is the cylinder a separate line, with its make, model and litres written down?
  2. Does the price include removing and disposing of the old cylinder?
  3. Where will the tundish and discharge pipe run, and has anyone checked it can reach outside?
  4. Is the installer G3 qualified, and who notifies Building Control?
  5. Will I get the Building Regulations certificate, and when?
  6. Is the mains pressure and flow being measured, or is it assumed?
  7. What is included if the old isolators or valves will not shut off?
  8. Who do I call if it drips or fails in the first year?

Get a fixed price for your cylinder

Tell us what you need and we call you back with a fixed price for replacement, repair, installation or service. No VAT added, no obligation.

We call you back to confirm details. No obligation. Prefer to talk? 0207 046 1363

Or call 0207 046 1363WhatsApp 07456 975436

Frequently asked questions

How much does it cost to replace a hot water cylinder in London?
Our fixed price is £1,450 for labour and miscellaneous parts on a like-for-like replacement, with the cylinder itself quoted as a separate line. A new installation or conversion, which includes pipework and Building Regulations work, is £2,400, again with the cylinder as its own line. Published UK guides put the all-in total at roughly £2,000 to £3,800 depending on the job.
How long does a cylinder replacement take?
A like-for-like unvented swap is typically half a day to a day. Converting from vented to unvented takes longer because the mains feed, discharge route and expansion vessel are new and the loft tank comes out. Access and the discharge route usually decide the time more than the cylinder does.
Should I repair or replace my hot water cylinder?
Repair if the fault is a valve, expansion vessel, thermostat, motorised valve or immersion element and the shell is dry. Replace if water is weeping from the tank, seams or base, if there is corrosion, or if components keep failing on an old unit. A £180 diagnosis settles it in writing before you spend on either.
Do I need a G3 qualified engineer?
Yes, for any unvented cylinder. Installing or modifying one is notifiable work under Part G of the Building Regulations, so the installer must be G3 qualified and either belong to a competent person scheme or notify Building Control. Ask for the certificate afterwards. Work without notification can cause problems with insurance and when selling.
Is my cylinder vented or unvented?
If there is a cold-water tank in the loft feeding it, it is vented. If there is a tundish (a small funnel on a discharge pipe) and an expansion vessel near the cylinder, and no loft tank, it is unvented. A cylinder fed straight from the mains with those two parts is unvented.
Is a dripping tundish an emergency?
A drip that starts while the water heats and stops when it cools is usually the expansion vessel and can wait for a booked repair. Steam, scalding water or a constant flow is different: switch off the heat source, keep clear and call an engineer straight away. Never block the discharge pipe.
What size hot water cylinder do I need?
A rule of thumb is 35 to 45 litres per person plus extra for a second bathroom or a daily bath. That is about 120L for a studio, 150 to 170L for a two-bed flat and 180 to 210L for a three-bed house. Mains flow and bathroom use at the same time matter as much as headcount, so we measure on the day.
How much does hot water cylinder repair cost?
Most repairs cost far less than a new cylinder. Typical figures from our earlier work are £180 to £280 for an expansion vessel, £120 to £160 for a temperature and pressure valve and £90 to £130 for an immersion element. The £180 diagnosis tells you which part has failed before any repair is quoted. We do not currently charge VAT.
How much does a hot water cylinder service cost?
An annual unvented cylinder service is £180 with no VAT added. It covers the expansion vessel pressure, relief valves, thermostats and discharge pipework, and updates the logbook manufacturers ask for to keep a warranty valid.
Who can install an unvented cylinder in London?
Only a G3 qualified plumber should fit one. Installation is notifiable under Part G of the Building Regulations, so the installer must be registered with a competent person scheme or notify Building Control. Our installation price is £2,400 labour and Building Regulations work, with the cylinder quoted separately.
How often does an unvented cylinder need servicing?
Once a year. Manufacturers usually make an annual service a condition of the warranty, and it covers the expansion vessel pressure, the relief valves, the thermostats and the discharge pipework. Our annual service is £180.
How long does a hot water cylinder last?
Many last 15 to 25 years. London's hard water and missed annual services shorten that, mainly through scale on elements and coils. A cylinder past 20 years that has started to fail is normally cheaper to replace than to keep repairing.
What warranty does a new cylinder come with?
It depends on the maker. Heatrae Sadia's Megaflo Eco is lifetime for the first domestic owner and 30 years on resale, Telford is lifetime, and Joule is 25 years on the vessel. All of them depend on registering the cylinder within 28 to 30 days and on an annual service, and scale damage is usually excluded. On top of the manufacturer's tank warranty, our workmanship is guaranteed for 12 months. Check the current wording for your model.
Is there a call-out fee?
Pre-booked cylinder work has no call-out fee. Same-day or out-of-hours emergency call-outs are £60 at any hour. The fixed prices on this page are what you are quoted for diagnosis, replacement, installation and service.

Hot water cylinder installation across London

We install, replace and repair hot water cylinders across all 32 London boroughs and the City, including Kidbrooke, Brockley, Penge, Crystal Palace, Greenwich, Woolwich, Clapham and Canary Wharf.

CamdenWestminsterIslingtonHackneyTower HamletsSouthwarkLambethWandsworthHammersmith & FulhamKensington & ChelseaHaringeyGreenwich

All cylinder services

Every cylinder job we carry out in London

Emergency Repairs London Ltd · Company No. 17120057 · £5M public liability · G3 qualified · 24/7 emergency line · 0207 046 1363

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