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ERLEMERGENCY REPAIRSLONDON
G3 qualified plumber installing a Megaflo Eco unvented hot water cylinder in a London property
G3 Qualified — 25-Year Tank Warranty

Megaflo Eco Replacement London

Like-for-like Megaflo Eco swaps from £1,745 fitted across all 32 London boroughs. G3 qualified engineers, Tundish + twin immersion to current spec, full Benchmark logbook handover, Building Regulations Part G3 notification on every install. Upgrades from pre-2014 Megaflo CL Indirect handled the same day.

Constant drip from the Tundish? Blowing the T&P every heat cycle? No hot water? Most Megaflo faults are fixed first-visit from van stock. Larger upgrade jobs surveyed and quoted in writing on the spot.

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£5M Public liability
G3 Unvented qualified
25yr Tank warranty
BS EN 12897 compliant
2hr Central London SLA
Quick Answer

A Megaflo Eco replacement in London runs £1,745–£2,845 fitted depending on size. Current production Megaflo Eco Plus and Eco SystemFit cylinders ship with a Tundish discharge, twin top + bottom immersion bosses, an external 18L expansion vessel and a 25-year tank warranty. Like-for-like swaps from a pre-2014 Megaflo CL Indirect are a 4–6 hour single-day job. Every install is G3 notified, Benchmark logbook completed and a Building Regulations Compliance Certificate posted within 30 days.

What is a Megaflo Eco?

The Megaflo Eco is Heatrae Sadia's current-production unvented hot water cylinder — the direct successor to the Megaflo HE and Megaflo CL Indirect ranges. Every Megaflo Eco Plus and Eco SystemFit unit built since 2014 ships with a duplex stainless steel inner vessel, an external Tundish discharge, twin top + bottom immersion bosses for backup or off-peak heating, and an external 18L expansion vessel pre-charged to 3.0 bar. It is the default specification for new-build London flats and the most-installed unvented cylinder in the UK in 2026.

The two big upgrades over the pre-2014 Megaflo CL are the Tundish + external vessel arrangement, and the twin immersion fit. The Tundish provides the visible air-break that Building Regulations Part G3 mandates between the T&P discharge and the safe termination outside — and it gives an engineer-friendly visual cue that the cylinder is dumping water. The twin immersion lets you wire a backup electric supply through the top boss (sized to draw the upper third of the cylinder for a recovery shower) and a primary off-peak Economy 7 supply through the bottom boss on direct models.

Megaflo Eco replacement work in London splits two ways. Like-for-like swaps are roughly 70% of the volume — a 2015–2020 Eco Plus reaching end-of-warranty or failing on the vessel, replaced with a new current-spec Eco Plus on the same footprint. Upgrades from pre-2014 Megaflo CL are the other 30% — older units with collapsed internal air-gaps that can't be safely recharged in situ. Both routes are handled the same way: G3-qualified survey, fixed written quote on site, single-day install, full G3 notification and Benchmark handover.

Megaflo generations — what you have and what to fit

Four production eras of Megaflo cylinder are still live in London airing cupboards in 2026. The data plate on the front of the unit tells you which generation you're looking at, and that decides whether the right call is repair, like-for-like or full upgrade.

Megaflo HE (pre-2008)

Heatrae Sadia's original badged Megaflo. Carbon-coated steel inner vessel, single immersion port, internal expansion bubble (no external vessel). Largely time-expired in 2026 — most need a full like-for-like replacement to the modern Eco.

Megaflo CL Indirect (2008–2013)

First duplex stainless model. Internal air-gap expansion (no external vessel), single immersion. Still seen in early 2010s London new-builds. Common fail point: factory air-gap collapses around year 10–12 and the cylinder discharges from the T&P.

Megaflo Eco Plus (2014–present)

Current production model. Duplex stainless inner with full external Tundish discharge, twin (top + bottom) immersion bosses for backup / off-peak heating, external expansion vessel pre-charged to 3.0 bar, BS EN 12897 compliant. 25-year tank warranty when serviced annually.

Megaflo Eco SystemFit

Pre-plumbed Eco variant supplied with factory-fitted inlet group, T&P, expansion vessel and tundish on a single bracket. Cuts install time by 1–2 hours. The default specification for new-build London flats since 2018.

Megaflo Eco Plus unvented cylinder with Tundish discharge and external expansion vessel

Megaflo Eco sizing guide

London sizing follows the Hot Water Association rule: 35–45 litres of stored hot water per occupant, plus 50 litres for every bath used daily. We oversize by one step where mains pressure is borderline, where there's a freestanding bath in the spec, or where future heat-pump pairing is on the cards.

PropertyRecommended modelFitted from
1-bed flat, 1 bathroom, 1–2 occupantsMegaflo Eco 125L£1,745
2-bed flat, 1 bathroom, 2–3 occupantsMegaflo Eco 145L£1,845
3-bed terrace, 1–2 bathrooms, 3–4 occupantsMegaflo Eco 170L / 210L£1,995 / £2,145
4-bed house, 2 bathrooms, 4–5 occupantsMegaflo Eco 210L / 250L£2,145 / £2,445
5+ bed house, 3 bathrooms, freestanding bathMegaflo Eco 300L£2,845
HMO / secondary circulation / heat-pump pairingMegaflo Eco 250L / 300L SystemReadyFrom £2,545

Megaflo Eco replacement cost — 2026 prices

Fixed prices given on site after a 10-minute diagnostic. Each figure below includes the cylinder, full inlet group, Tundish discharge to outside, primary or twin-immersion connections, removal and disposal of the old unit, Building Regulations G3 notification and the Benchmark logbook handover. No call-out fee on quoted work.

JobWhat's includedFitted from
Megaflo Eco 125L — like-for-like swapSupply & fit 125L Megaflo Eco Plus, full inlet group, Tundish discharge, twin immersion wiring, G3 notification, Benchmark logbook.£1,745
Megaflo Eco 145L — small family swapSupply & fit 145L Megaflo Eco Plus indirect, primary connections, expansion vessel, T&P, commissioning, certificate.£1,845
Megaflo Eco 170L — 3-bed terraceSupply & fit 170L Megaflo Eco Plus, full G3 group, removal & disposal of old unit, Building Control filing.£1,995
Megaflo Eco 210L — 4-bed / 2-bathSupply & fit 210L Megaflo Eco Plus, twin immersion connection, secondary return ready, full Benchmark handover.£2,145
Megaflo Eco 250L — large family / HMOSupply & fit 250L Megaflo Eco Plus, mains uprate check, discharge re-route if needed, full G3 paperwork.£2,445
Megaflo Eco 300L — premium / freestanding bathSupply & fit 300L Megaflo Eco Plus, full inlet group, twin immersion, commissioning, 25-year tank warranty registration.£2,845
Older Megaflo CL (pre-2014) → Eco upgradeRemoval of legacy Megaflo CL Indirect, replacement with current Eco model, new vessel + Tundish discharge route.From £1,945
Megaflo Eco repair — vessel / T&P / elementOn-site fault find, like-for-like vessel, T&P or twin immersion element replacement, recommissioning.£165–£295

* Prices include VAT and Building Regulations G3 notification. Full price list on the pricing page.

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Megaflo Eco install process — five steps

Every Megaflo Eco install follows the same sequence whether it's a like-for-like or an upgrade from a pre-2014 CL. Total time on site for a standard 170–210L like-for-like swap is 4–6 hours.

1

Isolate & drain old cylinder

30–45 min

Cold mains isolated at the inlet stopcock, electrical immersion supplies dead-tested and locked off, primary flow / return capped on indirect units. Old cylinder drained through the immersion boss to outside via temporary hose.

2

Strip out and remove legacy unit

45–60 min

Disconnect primary, secondary, cold-in, hot-out, T&P discharge and immersion cabling. Carry the old unit out — most pre-2014 Megaflos weigh 35–60 kg empty and need two engineers in mansion-block cupboards.

3

Pipe-up new Megaflo Eco

90–120 min

Mount the new Eco unit, fit the inlet group (PRV, check valve, strainer, expansion vessel), connect primary flow / return for indirect or hard-wire the twin immersion for direct. Tundish piped in 22 mm copper with continuous fall to an external visible termination.

4

Fill, vent & pressure-test

30–45 min

Open the mains slowly, vent through the highest outlet, hold at static pressure for 10 minutes, leak-check every joint. Set inlet PRV to 3.0 bar working pressure. Verify expansion vessel pre-charge with the cylinder drained.

5

Commission & certify

30–45 min

Heat to 60°C, witness-test the T&P valve lift, confirm energy cut-out function, log Benchmark commissioning entries, file G3 notification with Building Control via the Competent Persons Scheme. Compliance Certificate posted within 30 days.

G3 compliance & Benchmark commissioning

A Megaflo Eco install is a controlled service under Approved Document G3 of the Building Regulations. Every job is wrapped in the same compliance trail — the same way Heatrae Sadia, the warranty insurer and any future buyer's surveyor will expect to see it.

G3

Approved Document G3 — Hot water supply and systems

Every unvented hot water storage system over 15 litres in England and Wales is a controlled service under Building Regulations Part G. The engineer must hold a current G3 ticket (BPEC HWSS, LCL Awards or City & Guilds 6035), renewed every five years. The work must be notified to Building Control directly or via a Competent Persons Scheme.

Benchmark

HHIC Benchmark commissioning scheme

The Benchmark logbook ships inside every Megaflo Eco carton. The engineer completes the commissioning section on the day of install — recording inlet pressure, expansion vessel pre-charge, T&P lift test, energy cut-out test, immersion resistance, primary flow and return temperatures — and signs it off against the G3 ticket number. Heatrae Sadia's 25-year tank warranty is conditional on the Benchmark being completed and on annual servicing entries being added every 12 months.

BS EN 12897

Indirectly heated unvented closed storage water heaters

The European product standard governing cylinder construction and the layered safety devices required on every UK unvented cylinder — working thermostat, non-self-resetting energy cut-out, expansion device, and T&P relief valve discharging via a Tundish to a safe visible termination. Every component on a Megaflo Eco is certified against this standard.

CPS

Competent Persons Scheme — Building Control notification

ERL self-certifies every Megaflo Eco install via the WaterSafe / BESCA Competent Persons Scheme. The notification is filed with the relevant London borough within 7 days of completion, and a Building Regulations Compliance Certificate is posted to the property owner within 30 days. That certificate is what a future solicitor, surveyor or insurer will ask for at sale or renewal.

Common Megaflo Eco faults — worked examples

Five anonymised London jobs from the last twelve months. Same diagnostic, same fixed-price-on-site rule.

Tundish dripping on a 2017 Megaflo Eco Plus — Highbury

180L Eco Plus installed 2017, customer reported a constant drip into the Tundish during the heat-up cycle. Diagnosed as expansion vessel waterlogged — factory pre-charge had collapsed to 0.6 bar (target 3.0). External 18L vessel swapped, recharged, system rebalanced. Time on site: 90 minutes. Final invoice: £240 inc. VAT.

Pre-2014 Megaflo CL with internal air-gap failure — Clapham

2011 Megaflo CL Indirect, blowing the T&P every heat cycle. No external vessel — early CL models used an internal air-gap that collapses after 8–12 years. Cannot be recharged in situ. Customer offered like-for-like CL repair (not possible) or upgrade to current 170L Megaflo Eco Plus. Upgrade booked at £1,995 fitted with full G3 notification.

Twin immersion failure — landlord property, Tower Hamlets

2019 Megaflo Eco 145L on an EICR-flagged property. Bottom immersion element open-circuit, top element earth-leaking. Both Incoloy elements replaced (Megaflo factory part), thermostats reset to 60°C, RCD circuit re-tested to BS 7671. Recommissioning entry added to the Benchmark logbook. Cost: £295 inc. VAT.

Discharge route non-compliant — insurance survey, Kensington

2016 Megaflo Eco Plus 210L flagged on a buildings-insurance survey because the Tundish discharge ran horizontally into a soil stack — a Building Regulations breach. Re-piped in 22 mm copper from Tundish, continuous fall, external termination through the rear wall above the gully with a 300 mm air gap. G3 paperwork updated. Cost: £420 inc. VAT.

Full older Megaflo upgrade for heat-pump pairing — Wandsworth

Customer fitting a 7 kW air-source heat pump. Existing 2009 Megaflo CL Indirect had a small 1.6 m² coil — too small for the heat pump's flow temperatures. Upgraded to a Megaflo Eco SystemReady 250L with a 3.0 m² heat-pump coil, repositioned in the same cupboard. Two-day install. Cost: £2,945 inc. VAT.

Pre-2014 Megaflo dripping or blowing the T&P?

Older Megaflo CL units with collapsed internal air-gaps cannot be safely recharged in situ. A like-for-like upgrade to a current Megaflo Eco Plus restores the 25-year tank warranty and brings the discharge route up to current Building Regulations. Surveyed and quoted in writing on site.

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Areas covered across London

Megaflo Eco replacement carried out across every London borough, with heaviest call volumes from Camden, Westminster, Islington, Hackney, Wandsworth, Kensington & Chelsea and Hammersmith & Fulham. Same-day surveys in Zones 1–2.

CamdenWestminsterIslingtonHackneyTower HamletsSouthwarkLambethWandsworthHammersmith & FulhamKensington & ChelseaHaringeyGreenwich

Frequently asked questions

How do I tell which Megaflo I have?
The data plate is on the front of the cylinder near the immersion access cover. Models pre-2008 will say 'Megaflo HE' with a carbon-coated steel inner. Models from 2008–2013 are labelled 'Megaflo CL Indirect' or 'Megaflo CL Direct' with a duplex stainless inner but no external expansion vessel — the air-gap is internal. Current models (2014 onwards) are 'Megaflo Eco Plus' or 'Megaflo Eco SystemFit' and ship with a Tundish discharge, twin top + bottom immersion bosses and an external 18L expansion vessel. A photo of the data plate sent over WhatsApp gives us the exact serial and we can confirm parts availability in 60 seconds.
Do I need a G3 engineer to replace a Megaflo Eco?
Yes. Approved Document G3 of the Building Regulations makes unvented hot water cylinder installation, commissioning and modification a controlled service. The engineer must hold a current G3 (BPEC, LCL Awards or City & Guilds 6035) Unvented Hot Water Systems certificate and the work must be notified to Building Control directly or through a Competent Persons Scheme. A Megaflo Eco swap fitted by anyone without a G3 ticket invalidates the Heatrae Sadia 25-year tank warranty, voids the home insurance and exposes the owner to enforcement under the Building Act 1984.
Can a pre-2014 Megaflo CL be repaired or does it need replacing?
It depends on the fault. T&P or PRV failures on a pre-2014 Megaflo CL are still routine repairs from £165–£260 fitted. The terminal fault on these units is internal air-gap collapse — the factory expansion bubble inside the cylinder loses its charge and cannot be recharged in situ. Once that happens, every heat cycle blows the T&P. At that point the only economic fix is a full like-for-like replacement to a current Megaflo Eco Plus, which gives you a fresh 25-year tank warranty and an external vessel that can be re-charged annually.
Why does the new Eco have a Tundish and the old CL didn't?
All current Megaflo Eco Plus units ship with an external Tundish — a small clear plastic air-break between the T&P / expansion relief outlet and the discharge pipework. It's mandated by Building Regulations Part G3 and BS 6700, and it does two jobs: it gives a visual indication that the cylinder is dumping water (a constant drip = a fault), and it provides the air gap that prevents discharge water from being siphoned back into the cylinder. Pre-2014 Megaflo CL units had the air-break built into a sealed internal arrangement, which is why those models can't be safely recharged once the seal fails.
What's the difference between Megaflo Eco Plus and Megaflo Eco SystemFit?
Both are current production cylinders with identical inner vessels, twin immersion bosses and 25-year tank warranties. The Eco Plus ships loose — engineer fits the inlet group, T&P, expansion vessel and Tundish on site. The Eco SystemFit ships with all that pre-plumbed onto a factory bracket above the cylinder, which saves 1–2 hours of install time and gives a tidier finish. SystemFit is around £80 more on the cylinder cost but recovers most of that in labour. It's the default specification for new-build London flats since 2018.
How long does a Megaflo Eco replacement take?
A like-for-like swap in a flat with accessible pipework is a 4–6 hour single-day job. Two engineers handle the lift on anything 210L or larger because the empty cylinder weighs 40–60 kg. Re-routing the Tundish discharge to outside takes longer in mid-floor flats where the original installer hid it in a soil stack — that adds 1–2 hours. A full upgrade from a pre-2014 Megaflo CL with new external vessel and Tundish typically runs 6–8 hours. Larger 250–300L installs in mansion blocks with rooftop airing cupboards can stretch to a second day for access reasons.
Will the new Megaflo Eco work with my existing pipework?
On a like-for-like Megaflo CL → Eco swap, the cold inlet, hot outlet, primary flow / return and immersion cabling all align with the existing pipework. The two changes are the external expansion vessel (needs a 22 mm tee on the cold inlet) and the Tundish discharge — the new Eco needs a visible Tundish above the cylinder with a 22 mm discharge falling to an external termination. If the existing CL had a hidden internal discharge, that pipework needs re-routing as part of the install. The engineer surveys this before quoting.
What about the twin immersion — do I need to wire it up?
Modern Megaflo Eco Plus cylinders ship with two immersion bosses (top and bottom). On indirect models heated by your boiler, the immersions are a backup — wired through a single fused spur on a 16A circuit, used when the boiler fails. On direct (electric-only) models both immersions are wired live, typically on an Economy 7 tariff with the bottom element on the off-peak circuit and the top element on the peak. Twin wiring adds around £85–£140 to the install depending on whether the existing circuit needs an RCD upgrade to BS 7671 18th Edition.
What size Megaflo Eco do I need?
London sizing rule: 35–45 litres of storage per person plus 50 litres per regular bath. A 1–2 bed flat with a shower is fine on a 125–145L Eco. A 3-bed family home with one bath fits a 170L. A 4-bed with two bathrooms wants 210–250L. Anything with a freestanding bath, three or more bathrooms, or secondary circulation is 300L. We oversize by one step where mains pressure is borderline or where future heat-pump pairing is on the cards — a 250L Eco SystemReady with a 3.0 m² coil is the most futureproof spec for a London family home in 2026.
Is the Benchmark logbook really mandatory?
The Benchmark commissioning logbook ships in every Heatrae Sadia Megaflo Eco carton. It is required to validate the 25-year tank warranty — Heatrae Sadia's policy is that they will refuse a tank claim if the original commissioning section is blank or if there is no record of annual servicing within 12 months of each anniversary. The engineer completes it on site during commissioning and we keep a digital copy on file. If a Megaflo is sold with a property, the Benchmark logbook transfers with it and protects the new owner's warranty.
Do I have to notify Building Control for a Megaflo swap?
Yes — under Approved Document G3 every unvented cylinder install, replacement or material alteration is notifiable to Building Control. The easiest route in London is via a Competent Persons Scheme (WaterSafe, BESCA or APHC) — the G3 engineer self-certifies the work and the scheme files the notification with the relevant borough. The homeowner gets a Building Regulations Compliance Certificate posted by the scheme within 30 days, which is the document your solicitor or surveyor will ask for at sale.
How often does a Megaflo Eco need servicing?
Annually, as a condition of the 25-year tank warranty. Heatrae Sadia's service interval covers expansion vessel pre-charge check (3.0 bar target), T&P valve witnessed lift, PRV outlet pressure measurement, twin immersion resistance and thermostat test, anode inspection where fitted, Tundish discharge route check and a refreshed entry in the Benchmark logbook. ERL's annual G3 service is £155 fixed, with reminder emails on the anniversary month and bundled discounts for landlord portfolios.
What guarantee comes with a new Megaflo Eco install?
The cylinder carries Heatrae Sadia's 25-year tank warranty, contingent on annual G3 servicing. The factory-fitted components (immersions, T&P, PRV, expansion vessel) carry a 2-year parts warranty. ERL adds a 12-month workmanship guarantee on the install labour and a 90-day call-back on any commissioning-related issue at no charge. The Benchmark logbook and Building Regulations Compliance Certificate together form the proof of warranty if you ever come to sell the property.
Can a Megaflo Eco run a power shower at the same time as a bath?
Yes — that's the headline benefit of a properly sized unvented Eco over a vented cylinder with a loft tank. Both outlets run at full mains pressure (3.0–3.5 bar) with no flow-rate drop, provided the cold mains supply can deliver the simultaneous demand. The two checks we run before quoting are static inlet pressure (must be at least 1.5 bar dynamic, ideally 2+ bar) and the cold supply flow rate (typically 20+ L/min for a 4-bath house). Where mains is borderline we either uprate the incoming supply or fit a 300L Megaflo Eco with a higher coil rating for faster recovery.
Can a Megaflo Eco be installed in a top-floor flat?
Yes — they are common in London top-floor flats because they remove the need for a loft tank, cold feed and vent pipe. The two engineering checks are mains inlet pressure (minimum 1.5 bar dynamic at the inlet group, easily met in most modern London supplies) and a viable Tundish discharge route to outside. In some mansion blocks the discharge route is the harder problem — the cylinder may need to live closer to an external wall than the previous airing cupboard, or the discharge piped through a fire-rated metallic duct to comply with Part B compartmentation.

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Service area

Megaflo Eco engineers across all London boroughs

G3 qualified Megaflo specialists based in central London, with same-day cover across all 32 London boroughs and the City. Average response inside Zone 2 is 60 minutes for emergencies and 24–48 hours for booked surveys.

Completed Megaflo Eco G3 commissioning certificate and Benchmark logbook

Megaflo Eco replacement — quoted & fitted by London's G3 engineers

Fixed price on site, single-day install where possible, Building Regulations G3 notification filed, Benchmark logbook completed, 25-year tank warranty registered. £5M public liability, fully insured, 4.9★ across 184 verified reviews.

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