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A new boiler — a like-for-like swap or a change of type — is gas work and a job the Building Regulations control, so it has to be installed by a Gas Safe registered engineer who notifies the work. Find a verified one across the Square Mile, and know the gas-safety basics first.
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⚠️ Smell gas? Don’t touch electrical switches or use a naked flame; open doors and windows; from outside call National Gas on 0800 111 999 (24h). Suspect carbon monoxide? Switch the appliance off, get everyone out, call the same number and seek medical help. More in Safety first.
Contact verified Gas Safe boiler installers in the City of London ↓
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Coverage: EC1–EC4, E1 and the WC2A edge — the whole Square Mile, from Temple to the Tower fringe.
What this covers: new and replacement gas boilers — sizing and type (combi, system or heat-only), flue routing and clearances, condensate, gas supply, commissioning, and the Building Regulations notification a new boiler triggers.
Something else? A boiler that’s faulty rather than due for replacement is boiler repair; a routine service, or a landlord’s annual gas safety check, is boiler servicing; radiators, the pump and the wider system are central heating repair.
Costs: usually a fixed quote for the install after a survey — see what it costs.
Availability: plumbers set their own hours; check each listing for the cover they offer.
Jump to: Choosing & fitting · Installs in the City · Safety first · By district · Costs · FAQs
Choosing and fitting a new boiler
A good installer surveys first, then quotes — the boiler is only part of it.
Type and sizing. Combi, system or heat-only is the first decision, and it’s about the home, not just the old boiler: hot-water demand, the number of bathrooms, water pressure and whether there’s a cylinder. An oversized boiler wastes money; an undersized one struggles. See Combi vs System Boiler and, if you’re weighing a repair against a new unit, Boiler Repair or Replace.
Flue routing and clearances. A new or moved boiler needs a compliant flue position and the right clearances from windows, openings and boundaries. The Gas Safe Register notes a gas engineer must be able to examine the flue along its length, so a flue routed through a void or boxed-in space needs inspection hatches.36
Condensate. A modern condensing boiler produces condensate that needs a drain to a suitable waste; in a flat that’s about routing it internally where possible, since an external run can freeze in a cold snap.
Gas supply. The installer checks the gas supply and pipe sizing can feed the new boiler — a bigger or different boiler sometimes needs the gas pipework upgraded.
The Building Regulations notification. Installing or replacing a boiler is a heat-producing appliance job controlled under the Building Regulations, so the local authority must be notified. A Gas Safe registered installer self-certifies the work and notifies Building Control, and a Building Regulations Compliance Certificate — the “boiler installation certificate” — is then issued for the property.37 In the City, the local-authority building-control function sits with the City of London Corporation’s District Surveyor’s Office.12 Keep the certificate — you’ll need it if you sell or remortgage.
Commissioning and registration. A new boiler is commissioned to the manufacturer’s instructions (often recorded on a Benchmark checklist), and registering the installation usually activates the manufacturer’s warranty. It’s not the same as the annual service the boiler will need from year one — that’s boiler servicing.
Boiler installation in City flats: consent, communal heat and hard water
Installing a boiler in the City is mostly a flats job — the City of London Corporation counts around 8,600 residents against 678,000 workers in 1.12 square miles1 — and that changes what’s possible.
You may not have a gas boiler to replace. Some City homes have no gas boiler at all: Barbican flats use electric underfloor heating,4 and buildings on the Citigen heat network run from a shared supply, often via a heat-interface unit in the flat, rather than individual boilers.6 Where that’s the case, a private gas-boiler install may not be permitted or needed — worth confirming before you plan one.
Consent in a flat. A new flue terminal on a shared façade, or work that routes through communal areas, often needs freeholder or building-management consent — and a leaseholder usually needs to check the lease before changing or moving a boiler. Planning the flue and condensate route around the building is part of the survey.
Hard water and a new install. Thames Water says all the water in its region is hard, so scale builds up over time.7 On a new install it’s common good practice to protect the system — a system filter, an inhibitor and, where wanted, a scale reducer — so the new boiler isn’t working against scale and sludge from day one.
If you rent from the City of London Corporation, a boiler in a Corporation home is its to install and maintain as landlord — report a fault or a failing boiler on its repairs line, 0800 035 0003: the Corporation maintains communal areas and its own fittings inside the home, while tenants stay responsible for their own fittings or improvements, and work it isn’t obliged to do can be recharged.11
Safety first
A boiler runs on gas, so a few things matter more than the install itself.
If you smell gas or suspect a leak. Don’t turn any electrical switches on or off, don’t use naked flames or smoke, open doors and windows to ventilate, and turn the gas off at the meter control if you can reach it safely. If the smell is strong, leave the building — then call the National Gas Emergency Service on 0800 111 999 from outside. The line is open 24 hours.17
Carbon monoxide. CO is a colourless, odourless, tasteless gas that the HSE warns can be produced by any fuel-burning appliance, including a faulty boiler.19 National Gas lists symptoms to watch for — headaches, dizziness, nausea, breathlessness, light-headedness and drowsiness — and warning signs on the appliance itself: sooty marks or staining, a lazy yellow or orange flame instead of crisp blue, and a pilot light that keeps blowing out.17 If you suspect CO, switch the appliance off, open doors and windows, get everyone out, and from outside call National Gas on 0800 111 999 — then seek immediate medical help, because going out into fresh air won’t treat CO exposure on its own. Don’t go back in until it’s confirmed safe.17 Fit an audible CO alarm — a new install is a good moment to do it.
Who can install it. Installing a gas boiler must, by law, be carried out by a Gas Safe registered engineer — never a general handyman.15 That covers the gas-carrying parts, combustion, flue and the boiler’s sealed casing. The Gas Safe Register notes a purely non-gas component — say a water circulating pump or a control valve within the casing — can be handled by another competent tradesperson where no combustion-chamber seal is broken and no gas-carrying or combustion-controlling part is disturbed;35 but a full install is squarely Gas Safe work. For an oil or solid-fuel appliance, use a technician competent for that fuel.
The HSE advice line is not an emergency number. The HSE Gas Safety Advice Line, 0800 300 363, is for non-emergency gas safety information during office hours only (Monday to Friday) — it is not a substitute for the 24-hour National Gas emergency line.21
Find a verified Gas Safe boiler installer by district
In the City, what you can install depends heavily on the building.
Barbican & Golden Lane — estate flats on electric underfloor heating or communal heat may have no gas boiler to replace, so the heating type is the first thing to confirm.
Smithfield & the Farringdon edge — converted and mixed-use flats where a new flue position and condensate route have to be planned around the building.
Bank, Cornhill, Lombard Street & Mansion House — apartments above the offices where a flue terminal on a shared façade, or roof and riser access, may need freeholder or building-management consent.
Liverpool Street, Broadgate & Bishopsgate — modern blocks often on a communal heat network with heat-interface units, where a private gas-boiler install may not be permitted or needed.
Leadenhall, Fenchurch Street & Gracechurch Street — flats above commercial units where flue position, working hours and neighbour impact shape the install.
St Paul’s, Cheapside & Paternoster Square — flats where a like-for-like combi swap is common, with flue clearances to check.
Cannon Street, Queen Victoria Street & the riverside — compact flats where the condensate route and a sensible flue position need planning to avoid freeze-ups.
Portsoken & the Aldgate edge — the Middlesex Street and Mansell Street estates, where leaseholder or freeholder consent and the existing heating type shape what can be installed.
What it costs
A boiler install is usually a fixed quote after a survey. The ranges below are a rough sense-check, not a quote.
| Typical job | Editorial estimate |
|---|---|
| Combi boiler replacement (like-for-like swap) | £1,800–£3,000 |
| System or heat-only boiler replacement | £2,000–£3,500 |
| Change boiler type / reposition (new flue + pipework) | £2,500–£4,500+ |
| New or extended flue run | £150–£400 |
| Power flush before a new boiler | £350–£800 |
| System filter / scale protection on a new install | £120–£300 |
A weekday Square Mile visit can also carry the Congestion Charge of £18 a day and, for a non-compliant vehicle, the ULEZ charge of £12.50, depending on the vehicle, timing and route.1314 For weighing a repair against a replacement, see Boiler Repair or Replace.
Editorial estimate only — illustrative ranges to help you sense-check a quote, and they exclude the boiler model, any system upgrades and access works. They are NOT regulated rates, NOT market data, and NOT a published cost survey. Always get a written quote after a survey.
Frequently asked questions
Yes — a boiler is a heat-producing appliance controlled under the Building Regulations, so the local authority must be notified.
Your Gas Safe registered installer self-certifies and notifies Building Control.
A Building Regulations Compliance Certificate is issued for the property — keep it for selling or remortgaging.
It depends on hot-water demand, bathrooms, pressure and whether you have a cylinder, not just the old boiler.
See Combi vs System Boiler .
Often yes, but it means new flue and pipework.
In a flat, a new flue terminal or work through communal areas may need freeholder or building-management consent.
It’s common good practice, especially on an older system or with hard-water scale and sludge.
Many manufacturers expect the system to be clean and protected for the warranty to stand.
Yes.
An annual service keeps it running well and usually maintains the warranty.
A landlord still needs the annual gas safety check.
Both are boiler servicing, and separate from the installation certificate.
Maybe not.
Some City buildings run on a shared heat network via a heat-interface unit rather than individual boilers.
Check with building management before planning a gas-boiler install.
Why verified plumbers — not a general directory
A boiler install is gas work and a Building Regulations job, so the single most important check is Gas Safe registration — which is exactly what we confirm before a profile goes live.
Every listing is checked before it goes live and re-verified each year: we confirm the business is legitimately trading and verify the named contact, we check evidence of public liability insurance, and we confirm the plumber covers the City’s EC and edge postcodes before a profile is approved. For boiler and gas work, we confirm the engineer’s registration directly with the Gas Safe Register, and you can check any engineer there yourself. For work on the water supply, you can also look a plumber up on WaterSafe.
Profiles may be suspended or removed if credentials lapse or credible concerns are raised — see the full verification process →. No customer middleman fee: enquiries go directly to the plumber.
Related areas
Verified Gas Safe boiler installers across the City of London’s neighbourhoods, including:
- Bank
- Barbican
- Billingsgate
- Bishopsgate
- Botolph Lane
- Broadgate
- Cannon Street
- Carter Lane
- Cheapside
- Cornhill
- Fenchurch Street
- Fleet Street
- Golden Lane
- Gracechurch Street
- Guildhall
- Leadenhall
- Liverpool Street
- Lombard Street
- Mansell Street
- Mansion House
- Middlesex Street
- Monument
- Moorgate
- Old Bailey
- Paternoster Square
- Portsoken
- Queenhithe
- Smithfield
- St Paul’s
- Walbrook
Related services
Other verified plumbing services in the City of London:
- Emergency Plumber in the City of London
- Burst Pipes in the City of London
- Leak Detection in the City of London
- [Blocked Drains in the City of London](https https://verifiedplumbers.co.uk/london/city-of-london/blocked-drains/)
- Toilet Repairs in the City of London
- Tap Repair & Installation in the City of London
- General Plumbing in the City of London
- Bathroom Plumbing in the City of London
- Kitchen Plumbing in the City of London
- Washing Machine & Dishwasher Installation in the City of London
- Boiler Repair in the City of London
- Boiler Servicing in the City of London
- Central Heating Repair in the City of London
- Commercial Plumbing in the City of London
Related guides
- Combi vs System Boiler — A UK Guide 2026
- Boiler Repair or Replace? — A London Guide 2026
- London Plumbing Costs & Compliance Guide 2026
A new boiler is gas work, a Building Regulations job and — in a City flat — often a question of consent and what the building allows. Start with a verified Gas Safe engineer who’ll survey properly, install it right and notify the work — and if you ever smell gas, it’s National Gas on 0800 111 999 first.
Contact verified Gas Safe boiler installers in the City of London ↑
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Last reviewed: June 2026 by Adiel Khan — SFEDI-accredited business advisor, 20+ years’ experience (South East Enterprise Ltd) and operator of VerifiedPlumbers. LinkedIn ↗
This page is checked for compliance and regulatory accuracy against the bodies cited on this page, including the Gas Safe Register, National Gas, the HSE, Thames Water, the City of London Corporation and Transport for London. Source links are provided within this page where relevant.
Sources & further reading
- City of London Corporation — Our role in London (residents, workers, area) — https://www.cityoflondon.gov.uk/about-us/about-the-city-of-london-corporation/our-role-in-london
- City of London Corporation — Barbican Estate repairs and maintenance (electric underfloor heating) — https://www.cityoflondon.gov.uk/services/barbican-estate/barbican-estate-resident-information-pack/barbican-estate-repairs-and-maintenance
- E.ON — Citigen heat network (how heat networks work) — https://news.eonenergy.com/news/how-heat-networks-work-inside-londons-citigen-energy-network
- Thames Water — Hard water (regional hardness; limescale) — https://www.thameswater.co.uk/help/water-and-waste-help/water-quality/hard-water
- City of London Corporation — Report a repair, City of London estates (repairs line; landlord/tenant responsibility; rechargeable repairs) — https://www.cityoflondon.gov.uk/services/housing-and-homelessness/housing-services/report-a-repair-city-of-london-estates
- City of London Corporation — Contact Building Control / District Surveyor’s Office — https://www.cityoflondon.gov.uk/services/business-standards/building-control/contact-building-control
- Transport for London — Congestion Charge — https://tfl.gov.uk/modes/driving/congestion-charge/congestion-charge-zone
- Transport for London — Ultra Low Emission Zone (ULEZ) — https://tfl.gov.uk/modes/driving/ultra-low-emission-zone
- Gas Safe Register — official register of gas engineers (gas work must be done by a registered engineer) — https://www.gassaferegister.co.uk/
- National Gas — Emergency contacts (gas-smell steps; carbon monoxide procedure and symptoms; faulty-boiler signs; 0800 111 999) — https://www.nationalgas.com/emergency-contacts
- HSE — Carbon monoxide (colourless, odourless, tasteless; any combustion appliance) — https://www.hse.gov.uk/gas/domestic/co.htm
- HSE — Gas safety contacts (Gas Safety Advice Line 0800 300 363, office hours, non-emergency information only) — https://www.hse.gov.uk/gas/domestic/contacts.htm
- Gas Safe Register — Home gas safety / who can work on a gas appliance (non-gas component nuance) — https://www.gassaferegister.co.uk/gas-safety/home-gas-safety/home-improvements/
- Gas Safe Register — Flues in voids FAQs (engineer must be able to examine the flue; inspection hatches for concealed flues) — https://www.gassaferegister.co.uk/gas-safety/home-gas-safety/check-your-gas-appliances/flues-in-voids-faqs/
- Gas Safe Register — Building Regulations certificates (heat-producing appliance must be notified; installer self-certifies to the local authority; Building Regulations Compliance Certificate issued) — https://www.gassaferegister.co.uk/gas-safety/gas-safety-certificates-records/building-regulations-certificate/