Replacing a boiler is a major home investment — get the type, size and install right and it quietly pays you back for a decade or more. This page lists checked, insured Harrow Gas Safe engineers who supply and install gas boilers to standard.

✅ Checked before listing — identity, insurance, trading presence, Gas Safe (where relevant). How we verify →
✅ Workmanship guarantee badges on listings — 1, 3, 6 or 12 months

⚠️ Smell gas or suspect carbon monoxide? Don’t switch anything on or off, use no naked flames, open doors and windows, and call the National Gas Emergency Service on 0800 111 999 from outside. Safety steps ↓

Contact verified Gas Safe engineers in Harrow ↓

Coverage: Harrow and its HA postcodes — HA1, HA2, HA3, HA5 and HA7, plus the HA8/Edgware and Kenton/Queensbury edges.
What this covers: supplying and installing new and replacement gas boilers — combi, system and heat-only — including the controls, system flush, filter and flue work that come with a proper install. Listings show their own hours.
Not an install? A boiler that’s broken or faulting → Boiler Repair; the annual service or landlord gas check → Boiler Servicing; cold radiators or a sludged system → Central Heating Repair.
Costs: see what a new boiler costs — the boiler unit is on top of the install labour.

Jump to: Choosing & installing · Installing in Harrow · Safety first · By district · Costs · FAQs · Why verified engineers

Choosing and installing a new boiler

A good installation is mostly decisions made before anyone lifts a spanner — get them right and the boiler is efficient, reliable and properly covered by its warranty.

The right type. A combi heats water on demand with no cylinder, which suits smaller homes and saves space; a system or heat-only boiler with a hot-water cylinder suits larger homes or those with several bathrooms, where a combi can struggle to supply two showers at once. Flow rate matters in hard-water Harrow too. Our combi vs system guide weighs it up; a good installer sizes the boiler to the home rather than fitting the biggest or the cheapest.

Boiler Plus — the efficiency rules. New gas boilers in England must meet the Boiler Plus standard: a minimum ErP efficiency of 92%, and time and temperature controls on every install.³ A new combi must also include one of four energy-saving measures: flue gas heat recovery, weather compensation, load compensation, or smart controls with automation and optimisation.³ A reputable installer builds this in as standard.

The survey and the install itself. A good installer surveys before quoting — checking the incoming mains flow and pressure, hot-water demand and whether a cylinder is needed, gas pipe sizing, the condensate route and flue termination, and how clean the existing system is. Before a new boiler goes on an existing system, the system should be cleansed or power-flushed and a magnetic filter fitted — particularly important in Harrow (below), and often a condition of the manufacturer’s warranty. The flue has to be positioned to the rules, and an unvented hot-water cylinder, if fitted, is separately notifiable work needing a suitably qualified (G3) installer.

Notification and paperwork. Installing a boiler is notifiable building work; a Gas Safe registered installer can self-certify it under the Building Regulations, so you receive a Building Regulations compliance certificate, and they complete the Benchmark commissioning checklist in the boiler’s logbook — which your warranty usually depends on.² Keep both; you’ll want them when you sell. If your current boiler has simply broken, repair may be the better call first — see Boiler Repair.

Installing a boiler in Harrow: hard water, flues and the low-carbon option

Harrow’s water, its conservation areas and the move toward lower-carbon heating all bear on a new boiler.

Hard water makes the prep matter. Affinity Water records very hard water in Harrow North at 360 mg/l as calcium carbonate.¹ Scale and sludge can be a common contributor to boilers losing efficiency and failing early, so a proper Harrow install isn’t just the boiler — it’s a thorough system cleanse, a magnetic filter to catch debris, an inhibitor, and often a scale-reduction device on the mains. Before fitting, the installer should check for radiator cold spots and dirty system water to judge whether a chemical cleanse or a full power flush is needed. Skimping on this is a common false economy in a hard-water area.

Flues and conservation areas. Where a new flue or condensate pipe runs externally, its position has to meet the regulations — and in Harrow’s conservation areas, where an Article 4 direction can remove some permitted-development rights, the appearance and siting of visible external work may need extra care or consent from Harrow Council.⁸ Worth flagging to your installer if you’re in or near one of the borough’s conservation areas.

The low-carbon alternative. If you’re replacing a fossil-fuel boiler, a heat pump is the lower-carbon option, and the government’s Boiler Upgrade Scheme — administered by Ofgem — currently offers a £7,500 grant toward an air- or ground-source heat pump in England, claimed through an MCS-certified installer.⁷ A heat pump is a different installation from a gas boiler (and a different certification), but it’s worth knowing the option and the grant exist before you commit to like-for-like.

Gas work is Gas Safe by law. Installing a gas boiler must be done by a Gas Safe registered engineer — check the ID card.² A new boiler in a let property doesn’t remove the landlord’s duty to arrange an annual gas safety check thereafter — that’s Boiler Servicing.

Council tenants don’t arrange their own boiler installs — report heating problems to Harrow Council on 020 8901 2630.⁹

Safety first

A boiler is a gas appliance, so installation and the appliance it replaces both carry gas-safety duties.

If you smell gas or suspect a leak, the National Gas Emergency Service sets out the steps, in order:⁴

1. Don’t switch anything electrical on or off, use no naked flame, don’t smoke, and keep mobiles away from the suspected leak.
2. Open doors and windows if it’s safe to do so.
3. If the meter control valve is known and safely reachable, turn the gas off at the meter — unless the meter is in a cellar.
4. Leave if the smell is strong or you feel unwell.
5. Call the National Gas Emergency Service on 0800 111 999 from outside, and don’t return until a gas engineer gives the all-clear.

Carbon monoxide. A faulty or poorly installed gas appliance can produce carbon monoxide — a colourless, odourless gas. HSE notes that around 7 people a year die from CO poisoning caused by gas appliances and flues that have not been properly installed, maintained or are poorly ventilated, and that early symptoms — headaches, dizziness, nausea, breathlessness, collapse — can be mistaken for flu; it recommends a CO alarm compliant with BS EN 50291, sited per the manufacturer’s instructions.⁶ A new install is a good moment to fit or renew one. If a CO alarm sounds, or you suspect carbon monoxide: open doors and windows, switch the appliance off if it’s safe, leave the property, call the National Gas Emergency Service on 0800 111 999, and seek urgent medical advice if anyone may have been exposed.

Only a Gas Safe registered engineer should install a gas boiler — it’s both the law and the single best protection against an unsafe installation.

Find a verified boiler installer by district

The right boiler and install vary with the size and type of home. Use the search above, or browse below.

• Harrow on the Hill, Sudbury Hill & West Harrow — period and conservation-area homes where flue position and the appearance of external pipework may need extra care, and larger homes may suit a system boiler and cylinder.
• Pinner & Hatch End — established family houses where combi-to-system choices turn on the number of bathrooms and simultaneous hot-water demand.
• Harrow town centre & Station Road (HA1) — flats and mixed-use blocks, often suiting compact combi boilers, where the flue route, external wall access and any block-management consent need confirming before the install.
• Stanmore & Harrow Weald — larger homes that may need a system boiler with a cylinder to serve several bathrooms at once.
• Wealdstone — a mix of older terraces and newer flats, with a corresponding mix of boiler types and sizes.
• Kenton, Queensbury & the Edgware edge — boundary-area houses and flats where combi replacements are a common job.
• South Harrow & Roxeth — a mix of housing where like-for-like replacements with proper system prep are the staple.

Across the borough, the hard water makes a thorough system cleanse, a magnetic filter and a scale reducer the difference between a boiler that lasts and one that scales up early.

What a new boiler costs

A new boiler is the unit plus the install; system prep and controls add to it. The figures below are an editorial guide only.

Editorial estimate only. These are illustrative ranges to help you sense-check a quote — they are NOT regulated rates, NOT market data and NOT a published cost survey. The boiler unit itself varies widely by brand and model. A heat pump is a separate installation, typically costing more before the Boiler Upgrade Scheme grant.

One local factor: Harrow sits inside London’s Ultra Low Emission Zone, so a non-compliant van (up to 3.5 tonnes) pays a £12.50 daily charge to attend — heavier vehicles fall under the separate LEZ;¹⁰ Harrow is outside the central Congestion Charge zone, so that charge doesn’t apply.¹¹

Frequently asked questions

Why verified engineers — not a general directory

A boiler installation is a few thousand pounds and a decade of living with the result — and gas work that must, by law, be done by a Gas Safe registered engineer. The cut-price unregistered install is exactly the one that voids the warranty, fails Building Regs, and risks safety.

Every listing is checked before it goes live and re-verified annually: we confirm the business is legitimately trading and verify the named contact, we check evidence of public liability insurance, and we confirm the engineer covers Harrow’s HA postcodes before a profile is approved — and the workmanship guarantee shown on each listing stands behind the install. For gas work, we confirm Gas Safe registration with the Gas Safe Register; always ask to see the ID card, and ask for the Building Regulations compliance certificate and Benchmark record when the job’s done.²

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 engineer.

Related areas

Verified engineers across Harrow’s neighbourhoods, including:

• Belmont
• Canons Park
• Edgware
• Greenhill
• Harrow on the Hill
• Harrow Weald
• Hatch End
• Headstone
• Kenton
• North Harrow
• Pinner
• Pinner Green
• Pinner South
• Queensbury
• Rayners Lane
• Roxbourne
• Roxeth
• South Harrow
• Stanmore
• Wealdstone
• West Harrow

Related services

Other verified plumbing services in Harrow:

• Emergency Plumber in Harrow
• Burst Pipes in Harrow
• Leak Detection in Harrow
• Blocked Drains in Harrow
• Toilet Repairs in Harrow
• Tap Repair & Installation in Harrow
• General Plumbing in Harrow
• Bathroom Plumbing in Harrow
• Kitchen Plumbing in Harrow
• Washing Machine & Dishwasher Installation in Harrow
• Boiler Repair in Harrow
• Boiler Servicing in Harrow
• Central Heating Repair in Harrow
• Commercial Plumbing in Harrow

Related guides

• Combi vs System Boiler — UK Guide 2026
• Boiler Repair or Replace? — London Guide 2026
• Boiler Fault Codes Explained — London Guide 2026
• London Plumbing Costs & Compliance Guide 2026

A new boiler is one of the few home jobs where the decisions before the install — the right type and size, Boiler Plus controls, a proper system cleanse for Harrow’s hard water, and a registered engineer who notifies the work — matter as much as the boiler itself. The engineers listed here are checked for what matters: verified identity, evidence of insurance, and Gas Safe registration confirmed with the register, so the install is safe, compliant and guaranteed.

Contact verified Gas Safe engineers in Harrow ↑

← Back to all plumbing services in Harrow → verifiedplumbers.co.uk/london/harrow/

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 and regulations cited on it (Affinity Water, Gas Safe Register, GOV.UK Boiler Plus, the Gas Safety (Installation and Use) Regulations 1998, National Gas, HSE, Ofgem, Harrow Council and TfL). Source links are provided within this page where relevant.

Sources & further reading

1. Affinity Water — Harrow North (AF056) water-quality report 2025 (very hard water; 360 mg/l CaCO₃; scale in boilers and systems).
2. Gas Safe Register (legal requirement that gas work is done by a registered engineer; self-certification of installations under Building Regulations; check the ID card).
3. GOV.UK — Boiler Plus factsheet (minimum 92% ErP efficiency; time and temperature controls; additional combi measure — FGHR, weather/load compensation or smart controls).
4. National Gas — Emergency contacts (gas-emergency steps; 0800 111 999, 24/7).
5. The Gas Safety (Installation and Use) Regulations 1998 (governing regulations for gas installation, maintenance and use).
6. HSE — Carbon monoxide awareness (around 7 deaths a year; CO symptoms; CO alarm to BS EN 50291).
7. Ofgem — Boiler Upgrade Scheme (£7,500 grant toward an air- or ground-source heat pump in England, via an MCS-certified installer).
8. Harrow Council — Conservation areas (Article 4 directions can affect the appearance and siting of visible external work in conservation areas).
9. Harrow Council — Request a home repair (council-tenant repairs 020 8901 2630).
10. Transport for London — Ultra Low Emission Zone (ULEZ) (vehicles up to 3.5 tonnes; £12.50 daily charge; heavier vehicles fall under the LEZ).
11. Transport for London — Congestion Charge (central London zone only).