Replacing a boiler is a purchase most Londoners make once every 10-15 years. Prices range from £1,399 to £4,500+ depending on boiler type, property size, and installation complexity. The problem is that most websites give vague national averages that do not reflect London’s reality — congestion charges, higher labour rates, and the hard water that destroys boilers faster than elsewhere.
At boilerinstallerlondon.uk, we install 400+ boilers across London every year. We have fitted £1,800 budget combis in Croydon flats and £4,500 system boilers in 5-bed Hampstead houses. This guide gives you the exact prices we charge in 2026 — no hidden fees, no surprises, no fluff.
What a new boiler costs in London (2026)
London prices run 15-20% higher than the UK average. Congestion charges, ULEZ fees, parking restrictions, and higher labour rates all push costs up. Here is what you will actually pay:
| Boiler type | Property size | kW range | Supply + fit price | Time to install |
|---|---|---|---|---|
| Budget combi (Ideal Logic+, Baxi 600) | 1-2 bed flat | 24-28 kW | £1,800 – £2,400 | 1 day |
| Mid-range combi (Worcester Greenstar 4000, Vaillant ecoTEC Plus) | 2-3 bed house | 28-35 kW | £2,200 – £3,200 | 1 day |
| Premium combi (Worcester Greenstar 8000, Vaillant ecoTEC Plus 938) | 3-4 bed house | 30-40 kW | £2,800 – £4,000 | 1 day |
| System boiler (Worcester, Vaillant, Ideal) | 3-5 bed house | 30-40 kW | £2,500 – £3,500 | 1-2 days |
| Regular boiler (heat-only) | 4+ bed / old system | 35-42 kW | £2,200 – £3,200 | 1-2 days |
| Commercial boiler (40-100 kW) | Office, restaurant, care home | 40-100+ kW | £3,500 – £8,000+ | 2-4 days |
These prices include the boiler unit, flue, magnetic filter, labour, Gas Safe certification, and 10-year warranty registration. They do not include power flushes, pipe upgrades, or building regulation applications — we cover those separately below.
Combi vs system vs regular: which costs what?
The boiler type is the single biggest price driver. Most Londoners overpay by choosing the wrong type for their property.
| Factor | Combi Boiler | System Boiler | Regular (Heat-Only) Boiler |
|---|---|---|---|
| Best for | 1-3 bed, 1-2 bathrooms | 3+ bed, 2+ bathrooms | Older homes with existing tanks |
| Hot water | Instant, no tank | Cylinder required | Cylinder + cold water tank |
| Space needed | Small (wall-mounted) | Medium (cylinder cupboard) | Large (loft for tanks) |
| Install cost London | £1,800 – £4,000 | £2,500 – £3,500 | £2,200 – £3,200 |
| Efficiency | Up to 94% | Up to 94% | Up to 89% |
| Running cost | Lower for small homes | Lower for large homes | Highest |
| London suitability | Flats, small houses | 3+ bed houses | Replacement only |
Our recommendation: Go combi for 1-3 bed properties with 1-2 bathrooms. Go system for 3+ beds or homes with 2+ bathrooms where simultaneous showers are common. Only choose regular if you are replacing an existing open-vent system and do not want to re-pipe.
What size boiler do you need? The kW guide
Oversizing is the most common mistake we see. A 40 kW combi in a 2-bed flat wastes gas, short-cycles the boiler, and voids your warranty. Here is the correct sizi
| Property size | Radiators | Bathrooms | Recommended kW | Boiler type |
|---|---|---|---|---|
| Studio / 1-bed flat | 4-6 | 1 | 24-27 kW | Combi |
| 2-bed flat / small house | 6-10 | 1 | 28-30 kW | Combi |
| 3-bed house | 10-12 | 1-2 | 28-35 kW | Combi or system |
| 3-bed house (2+ baths) | 12-15 | 2-3 | 32-40 kW | System |
| 4-bed house | 12-15 | 1-2 | 32-38 kW | System |
| 4-bed house (3+ baths) | 15-20 | 3+ | 35-42 kW | System or regular |
| 5+ bed / large home | 20+ | 3+ | 42-50 kW | System (multi-zone) |
Quick formula: Multiply radiators by 1.5 kW, add 3 kW per bathroom, add 10% buffer. Example: 12 radiators + 2 bathrooms = (12 × 1.5) + (2 × 3) = 18 + 6 = 24 kW + 10% = 26.4 kW → choose 28-30 kW.
Brand prices: what you actually pay installed
| Brand | Model range | Typical install cost London | Warranty | Best for |
|---|---|---|---|---|
| Worcester Bosch Greenstar 4000 | 25-35 kW combi | £2,200 – £2,800 | 10 years | All-round reliability, parts availability |
| Worcester Bosch Greenstar 8000 | 30-40 kW combi | £2,800 – £3,500 | 10 years | Large homes, premium build quality |
| Vaillant ecoTEC Plus | 25-38 kW combi/system | £2,200 – £3,000 | 10 years | Quiet operation, energy efficiency |
| Ideal Logic+ | 24-35 kW combi | £1,800 – £2,400 | 7 years | Budget-conscious, solid warranty |
| Ideal Vogue Max | 26-40 kW combi/system | £2,200 – £3,000 | 12 years | Best warranty value, modern design |
| Baxi 600/800 Series | 25-36 kW combi | £1,900 – £2,600 | 10 years | Compact installs, cupboard fitting |
| Viessmann Vitodens 100-W | 26-35 kW combi | £2,200 – £2,800 | 10 years | German engineering, long-term reliability |
| Alpha E-Tec | 28-33 kW combi | £1,800 – £2,400 | 7 years | Entry-level, budget option |
We are not tied to any brand. We recommend what suits your property, budget, and hot water demand. Worcester Bosch and Vaillant dominate the UK market for good reason — parts are stocked same-day in every London borough, and Gas Safe engineers are trained on them extensively.
Hidden costs that add £500-£1,500 to your bill
Most quotes do not include these. We itemise everything upfront so you know the total before work starts.
| Extra work | When needed | Typical cost |
|---|---|---|
| Power flush (system cleaning) | System over 5 years old, sludge, cold radiators | £450 – £700 |
| Magnetic filter (Magnaclean / Sentinel) | Always recommended for new boilers | £120 – £150 |
| Gas pipe upgrade (15mm to 22mm) | Old properties, boilers over 28 kW | £200 – £400 |
| Flue repositioning | New boiler location, building regulations | £150 – £300 |
| Condensate pipe rerouting | Frozen pipe risk, new route needed | £80 – £150 |
| Building regulations application | New boiler type, location change | £100 – £200 |
| Scaffolding (flats above ground floor) | External flue access required | £200 – £500 |
| Removal of back boiler | Old properties with back boilers | £300 – £600 |
| Smart thermostat (Hive / Nest / Tado) | Upgrade heating controls | £150 – £250 |
| Scale reducer (hard water areas) | London water hardness 250-300 mg/L | £80 – £120 |
Our advice: Budget 10-15% extra for hidden costs. A £2,500 combi installation often becomes £2,800-£3,000 with power flush and filter. We tell you this during the free survey — not after work starts.
Boiler finance: how to spread the cost
Not everyone has £3,000 available. We offer 0% APR finance over 2-10 years subject to status.
| Boiler cost | Deposit | Monthly payment (10 years) | Total payable |
|---|---|---|---|
| £2,000 | £0 | £16.67/month | £2,000 |
| £2,500 | £0 | £20.83/month | £2,500 |
| £3,000 | £0 | £25.00/month | £3,000 |
| £3,500 | £0 | £29.17/month | £3,500 |
| £4,000 | £0 | £33.33/month | £4,000 |
Alternative options: pay monthly plans from £15/month with deposit, buy now pay later (12 months deferred), or split payment (50% upfront, 50% on completion).
How to get an accurate quote: the free survey process
Online calculators give rough estimates. A proper survey gives a fixed price that will not change.
Step 1 — Book free home survey Call us or book online. We visit at your convenience, including evenings and Saturdays. No obligation, no pressure.
Step 2 — Assessment (30-45 minutes) Our Gas Safe engineer checks:
- Current boiler type, flue position, pipework condition
- Gas supply pipe diameter (15mm vs 22mm)
- System pressure and sludge level
- Hot water demand (bathrooms, showers, occupancy)
- Best boiler location and any access issues
- Building regulation requirements
Step 3 — Fixed price quote You receive a written quote the same day. It includes boiler model, all labour, parts, extras, and warranty details. The price is fixed — it does not change unless you add work.
Step 4 — Installation day Most combi swaps take 1 day. System conversions take 1-2 days. We protect floors, clean up, and walk you through the new controls before leaving.
Step 5 — Warranty registration We register your 10-year warranty with the manufacturer. You get a digital service record and reminder for annual servicing.
Expert tips: how to avoid overpaying
| Tip | Why it matters | Potential saving |
|---|---|---|
| Get 3 quotes, compare like-for-like | Boiler model, warranty, extras, labour — not just headline price | £200-£500 |
| Book in summer (May-September) | Engineers quieter, sometimes 5-10% discounts | £100-£300 |
| Keep your existing flue position | Repositioning adds £150-£300 | £150-£300 |
| Do not oversize | 40 kW in a 2-bed flat wastes gas and money | £200-£400 on boiler |
| Combine with power flush | Doing both together saves £50-£100 vs separate visits | £50-£100 |
| Ask about ex-display boilers | Slight cosmetic damage, full warranty, 15-20% off | £300-£600 |
| Check for local council grants | Some boroughs offer energy efficiency grants | Up to £1,000 |
Common mistakes Londoners make
| Mistake | Why it hurts | What to do instead |
|---|---|---|
| Choosing cheapest quote without checking extras | £1,800 quote becomes £2,500 with hidden costs | Get itemised quotes, ask about power flush/pipe upgrades |
| Ignoring water hardness | Limescale destroys heat exchangers in 3-5 years | Install scale reducer, consider water softener |
| Not checking engineer’s Gas Safe ID | Illegal install, void insurance, safety risk | Verify on Gas Safe Register website |
| Buying online, fitting separately | No warranty if not installed by accredited engineer | Use accredited installer with manufacturer partnership |
| Skipping annual service | Warranty void, efficiency drops, breakdowns | Book annual service (£89-£109), set reminder |
FAQ
How much does a new boiler cost in London?
£1,800 for a budget combi in a small flat. £2,200-£3,200 for a mid-range combi in a 2-3 bed house. £2,500-£4,000 for a system boiler in a 3-5 bed house. Commercial properties: £3,500-£8,000+. Prices include supply, fitting, flue, filter, and certification.
How much to install a new combi boiler in London?
£1,800-£2,400 for budget models (Ideal Logic+, Baxi 600). £2,200-£3,200 for mid-range (Worcester Greenstar 4000, Vaillant ecoTEC Plus). £2,800-£4,000 for premium (Worcester Greenstar 8000, Vaillant 938). Add £450-£700 for power flush if needed.
Is it worth replacing a 15 year old boiler?
Yes — if repair costs exceed 50% of a new boiler. A 15-year-old boiler runs at 60-70% efficiency vs 94% for new condensing models. You save £200-£400/year on bills. With 0% finance, monthly payments often match your energy savings.
What is the cheapest boiler to install in London?
Ideal Logic+ 24 kW combi from £1,800 installed. Baxi 600 Series 24 kW from £1,900. These are reliable budget options with 7-10 year warranties. Avoid unknown brands — parts availability and engineer training are poor.
How long does boiler installation take in London?
Combi swap (same location): 1 day. Combi swap (new location): 1-2 days. System to combi conversion: 2-3 days. Regular to system: 1-2 days. Power flush adds 4-8 hours.
What size boiler do I need for a 3 bedroom house in London?
28-35 kW combi for 1-2 bathrooms. 32-40 kW system boiler for 2+ bathrooms or high hot water demand. Count radiators (1.5 kW each) and add 3 kW per bathroom.
Do I need a power flush with a new boiler?
Yes — if your system is over 5 years old or radiators have cold spots. Manufacturers require evidence of system cleaning to validate warranties. Installing a £3,000 boiler on a sludged system is like fitting a new engine into a car with a blocked radiator.
Can I get a new boiler on finance?
Yes — 0% APR over 2-10 years subject to status. From £15/month with deposit. Buy now pay later options available. We arrange finance during the free survey.
Get your fixed-price quote today
Boilerinstallerlondon.uk has installed 400+ boilers across London since 2015. Our Gas Safe engineers are accredited installers for Worcester Bosch, Vaillant, Ideal, and Baxi. Every quote is fixed, itemised, and honest — no hidden costs, no pressure.