#TeamOfPeople

A Gravity-Fed to Combi Conversion: A Vaillant Boiler Upgrade in Hackney

Project Overview

Plumb London converted an ageing gravity-fed heating system to a modern, mains-pressure combi system at a private home in Hackney, E9, installing a new Vaillant ecoFIT Pure 825 combi boiler. The original Potterton boiler was a non-condensing, heat-only unit long past its efficient working life, with no mains-pressure hot water. Following a full survey, our engineers removed the old boiler, hot water cylinder and loft tanks, carried out a full system powerflush, and commissioned a high-efficiency combi system with smart heating controls. The works were completed over a planned two-day programme, on time, on 17 June 2026, and to the client’s full satisfaction.

Contact Us
Image link

The Client’s Brief

The client’s objectives were clear from the outset:

  • Replace an outdated, inefficient non-condensing boiler with a modern, high-efficiency alternative
  • Improve hot water performance and consistency throughout the property
  • Remove the bulky cold water storage cisterns and hot water cylinder, freeing up loft and airing cupboard space
  • Introduce smart heating controls to improve comfort and reduce running costs
  • Achieve a noticeably higher standard of care and finish than a previous provider had delivered

During the consultation the client also learned that Plumb London undertakes bathroom and kitchen renovations — an offering they had been unaware of, and one relevant to their longer-term plans for the property.

Our Survey & Recommendations

Our senior Gas Safe engineer, Andrew, attended site on 8 May 2026 to carry out a full inspection and produce a detailed scope of works. The key findings and recommendations were:

The existing Potterton boiler was a non-condensing, heat-only gravity-fed system — inefficient by modern standards, with no mains-pressure hot water delivery.

The gas meter sat adjacent to the boiler location, giving an ideal gas flow rate for the new installation with no supply upgrade required.

Two cold water storage cisterns in the loft, plus a feed and expansion tank, were all confirmed suitable for decommissioning as part of the combi conversion.

A horizontal flue was the most practical and aesthetically sound exit route for the new boiler.

A condensate pump, routed through the loft into the existing bathroom waste, was recommended as a neat, compliant solution given the boiler’s internal location.

Eight radiators were assessed as suitable for retention, with new thermostatic radiator valves to be fitted.

A full system powerflush was recommended before installation, to remove accumulated sludge and magnetite — essential for protecting the new boiler and maintaining warranty validity.

Contact Us

Planning & Preparation

Following the survey, the client received a detailed written quotation covering the full scope of works and took time to review the proposal — a considered approach we fully support on projects of this scale. With the scope agreed, works were scheduled to commence on 16 June 2026, around six weeks after the initial visit, allowing the installation to be properly planned and resourced.

The Work We Carried Out

Across a two-day programme, Plumb London:

  • Isolated supplies and drained down the system as required
  • Decommissioned the old Potterton boiler, flue, hot water cylinder, loft tanks and associated components
  • Capped all redundant pipework and converted the stored hot water system to a mains-pressure combi configuration
  • Ran new hot water pipework from the cylinder cupboard, through the loft, and down to the new boiler location
  • Set out new cold water supplies on the optimal route, confirmed with the client before commencement
  • Carried out a full system powerflush in accordance with BS 7593
  • Supplied and installed a Vaillant ecoFIT Pure 825 combi boiler, with a 10-year manufacturer’s warranty
  • Supplied and fitted a new horizontal flue to current standards
  • Altered and connected pipework to suit the new boiler position
  • Completed all plumbing and electrical connections
  • Installed a new condensate pump, routed through the loft into the bathroom waste
  • Fitted a Vaillant 22mm boiler protection filter on the return and a 15mm inline scale reducer on the incoming mains
  • Supplied and fitted eight sets of thermostatic radiator valves with lock shields
  • Refilled the heating system and dosed with scale inhibitor
  • Wired the boiler to Part P and Part L requirements
  • Supplied and fitted a Honeywell T6R wireless smart thermostat and a new carbon monoxide alarm
  • Tested the existing gas supply for tightness, and balanced the system for even heat emission
  • Demonstrated all new controls and system functions to the client
  • Commissioned the installation, completed Benchmark documentation, registered the works with Gas Safe and notified Local Building Control
  • Removed all waste and left work areas clean and tidy

A formal testimonial was not obtained for this project; the client confirmed they were fully satisfied with the completed works.

Timeline & Completion

The installation was carried out by Andrew, our senior Gas Safe engineer, with Nikola. The survey took place on 8 May 2026; works ran from 16 to 17 June 2026 — a two-day programme delivered on time, with no material delays. The home was fully operational with its new system by the close of the second day.

Challenges & How We Solved Them

Condensate disposal. With the boiler in an internal cupboard and no accessible external drain nearby, our engineer designed a condensate pump solution discharging unobtrusively through the loft into the existing bathroom waste — a clean, Building Regulations-compliant outcome that also avoids the freezing risk associated with external condensate runs.

Conversion complexity. Converting from a gravity-fed, vented system to a fully pressurised combi requires careful planning of pipe routes, the decommissioning of multiple components, and precise reconfiguration of the distribution layout. We mapped the optimal hot and cold pipework routes and agreed them with the client before any cutting or chasing began, keeping disruption to a minimum.

System contamination. Older gravity-fed systems carry an inherent risk of sludge and magnetite in the pipework and radiators. A full powerflush to BS 7593 was completed before commissioning — protecting the new boiler, maintaining the manufacturer’s warranty, and extending the working life of the whole system.

Loft tank decommissioning. The loft held two cold water cisterns plus a feed and expansion tank, a common legacy arrangement in older London properties. All three were drained, disconnected and removed, with pipework capped cleanly — reclaiming considerable usable loft space for the client.

Contact Us

The Finished Result

The completed installation is a significant upgrade in every measurable regard. The home now runs on an efficient, mains-pressure system that responds instantly to demand — no waiting for stored water to reheat, and no cold spots from low-pressure delivery. The Vaillant ecoFIT Pure 825, one of the most reliable and efficient combi boilers on the UK market, is backed by a ten-year manufacturer’s warranty, available because Plumb London is a Vaillant Advance accredited installer. Paired with the Honeywell T6R wireless smart thermostat, the client controls heating schedules and temperature from a single device, including remotely, while thermostatic radiator valves throughout allow room-by-room control and reduce waste. A new carbon monoxide alarm adds a further layer of safety. With full commissioning, Benchmark documentation, Gas Safe registration and Building Control notification all completed, the client has complete peace of mind from a compliance and insurance perspective.

Project Investment

The complete gravity-fed to combi conversion was delivered for a fixed price of £5,580 including VAT. For the scope involved — removing an entire stored-water system, converting to mains pressure, a full powerflush, smart heating controls and a new high-efficiency Vaillant combi — this represented a sound long-term investment: lower running costs, reclaimed loft and cupboard space, improved hot water performance, and a ten-year manufacturer’s warranty in place of an ageing, inefficient system.

Need a Plumber? Call - 020 7871 1861

Plumb London can help fix your plumbing problems from fixing leaks to replacing boilers.

Why Choose Plumb London

  • Specialist expertise across plumbing, heating and refurbishment. Every project is surveyed, specified and commissioned by experienced engineers, with Gas Safe registration and Benchmark certification as standard on relevant work.
  • Accredited installers. As a Vaillant Advance accredited installer and a Gas Safe registered company, our work meets manufacturer and regulatory standards — and qualifies your installation for extended manufacturer warranties.
  • Quality that lasts. We install trusted manufacturer equipment, protect it properly — system flushing, filtration and correct commissioning — and register warranties so you are covered for the long term.
  • Respect for your home. Where access, layout or original features are a concern, we find a solution that protects the property rather than the quickest route for us.
  • Clear and accountable. Agreed scope, fixed pricing and a clean, planned handover — the same standard on every job, large or small.

Frequently Asked Questions

What is involved in converting a gravity-fed system to a combi boiler?

A conversion means removing the old boiler, the hot water cylinder and the cold water storage tanks, then reconfiguring the pipework to run at mains pressure before fitting the new combi. The system is powerflushed and commissioned. Depending on the property’s layout, this typically takes one to two days.

Will switching to a combi free up space in my loft and airing cupboard?

Yes. A combi heats water on demand, so the stored hot water cylinder and the loft cold water tanks are no longer needed and can be removed — often reclaiming an entire airing cupboard and a useful amount of loft storage.

Do I really need a powerflush when fitting a new boiler?

On an older system, yes. A powerflush to BS 7593 clears the sludge and magnetite that build up over years. Skipping it risks blockages and reduced efficiency in the new boiler, and can invalidate the manufacturer’s warranty.

Will a combi boiler improve my hot water pressure?

In most cases, yes. Combi boilers deliver hot water at mains pressure, removing the weak, gravity-fed flow common to older stored-water systems. The final result depends on the incoming mains pressure and flow rate at the property, which we check during the survey.

Gallery

2989 Happy Customer Reviews

Customer Testimonials

We are rated 4.8 of 5 stars

Don’t just take our word for it, here’s a selection of the latest reviews. You can view more here.

Contact Plumb London

If you are facing a plumbing, heating, boiler or drainage issue in London, do not hesitate to get in touch with Plumb London. Our friendly and knowledgeable team is ready to assist you with all your plumbing needs. Reach out to us today to schedule a consultation and experience the difference with Plumb London.

Contact Us
call-plumb-london-today