The honest version of the question “how much is a new boiler?” is “how much is this boiler, in this property, with this existing system?” The headline numbers in the showrooms assume a like-for-like swap on a tidy install. Real houses in Kent — with their Victorian risers, back-boilers behind chimney breasts, and condensate runs you can’t see until the boxing comes off — almost always need a little more than that. This is a working engineer’s 2026 price guide. Real ranges, real reasons prices move, and what you can do to keep yours on the lower end.
1. Combi boilers — the most common Kent install
For three-quarters of homes in Sevenoaks, Tonbridge and the surrounding postcodes, a combi replacement is the right answer. They’re compact, instant hot water, no airing-cupboard tank to lose. The 2026 fitted price range for a like-for-like Kent swap:
- Worcester Greenstar 30i / 35i: £2,400–£2,900
- Vaillant ecoTEC plus 832 / 835: £2,600–£3,000
- Baxi Platinum / 800 series: £2,200–£2,700
- Ideal Vogue Max: £2,500–£2,900
- Viessmann Vitodens 100-W: £2,700–£3,200
Like-for-like means: same fuel, same position on the wall, gas pipe and flue routes unchanged, cylinder already absent. As soon as the position moves or pipework changes, you’re adding cost — not because the boiler is different but because the labour goes up.
2. System boilers — for high-demand homes
Larger family homes with two bathrooms, or homes with strong shower demand, often work better with a system boiler plus unvented cylinder. Hot water comes out of mains pressure from the cylinder, so two showers can run at once without the temperature ducking. Fitted price for a Kent system swap:
- Worcester Greenstar Si Compact 30: £2,800–£3,400
- Vaillant ecoTEC plus 825: £3,000–£3,500
- Worcester / Megaflo unvented cylinder (180–210 L): add £900–£1,400
- Full system swap with new cylinder: £3,800–£4,800 fitted
3. Regular (heat-only) to combi conversion
A lot of older Kent housing stock still runs regular (heat-only) boilers with cold-water tanks in the loft and hot-water cylinders in the airing cupboard. Switching to a combi frees up the cupboard, removes loft tanks, and ends standing-pilot losses — but it’s a bigger job. Typical Kent fitted price £3,500–£5,500 depending on:
- Removal of loft tanks and pipework
- Removal of hot-water cylinder and airing-cupboard reinstatement
- Mains supply check — combis need 15–20 litres per minute flow at the kitchen tap
- Whether existing radiators are sized for combi pressure
We do a flow-rate test at survey. If the mains pressure or flow isn’t adequate for the combi size needed, we’ll say so — either upgrading the mains feed via the water board, or recommending a system boiler instead.
4. Air-source heat pumps — net cost after the grant
The Boiler Upgrade Scheme pays up to £7,500 toward an air-source heat pump in England and Wales (subject to MCS-certified install). In 2026 the typical Kent install is:
- Headline install cost: £14,000–£18,000 (Daikin Altherma, Mitsubishi Ecodan, Vaillant aroTHERM)
- Net cost after BUS grant: £6,500–£10,500
- Plus, if needed: radiator upsizing £800–£2,000; hot water cylinder £1,200–£1,800; insulation upgrades varied
Heat pumps work brilliantly in well-insulated Kent homes — particularly post-2010 builds or thoroughly retrofitted older houses. They underperform in leaky uninsulated solid-wall properties. We’ll always do a heat-loss calc before quoting. See our heat pump grants guide for the application detail.
5. What pushes the price beyond the from-figure
Four things, in order of how often we see them:
- Changing boiler position — relocating the flue, running new gas + condensate, possibly extending mains water. Adds £400–£900.
- Power flush — needed when an old system is sludged. Without it, the new boiler’s warranty is at risk. Adds £350–£600 depending on system size.
- Gas pipe upsize — older properties often have 15 mm gas pipework that won’t feed a 30 kW combi. Upgrade to 22 mm typically adds £200–£500.
- Flue work — high horizontal runs, vertical flues through roofs, awkward through-walls. Scaffold may be needed; total cost £300–£1,200.
6. Boiler grants and ECO4 in Kent
Two grant routes worth knowing about beyond BUS:
- ECO4 — for households on certain benefits, can fund the full boiler replacement on properties with EPC D–G. Eligibility is benefits-based; check with us at survey.
- Great British Insulation Scheme — covers loft and cavity-wall insulation up to certain limits, which is often the prerequisite to a heat pump performing well.
Kent local authorities also occasionally run top-up grant schemes — we keep an eye on these for clients in Sevenoaks DC, Tonbridge & Malling, Tunbridge Wells and Maidstone.
7. What “from £1,800” ads on Google actually mean
You’ll see headline prices well below the ranges above. They’re usually:
- Boiler-only, no fitting
- Pre-pay finance offers where the headline reflects the deposit, not the total
- A 24 kW entry-model in the smallest property, like-for-like, with no flush
- National brands with subcontracted fitters who never see the house before the day
Fair pricing for fitted work in Kent in 2026 starts around £2,200 for a true like-for-like combi swap with a small reputable installer. If a national brand quote sits at £3,200 and a local Gas Safe engineer quotes £2,400 for the same scope, the £800 difference is the brand markup, not better work.
8. Service contract savings
A few of the manufacturer warranties (Worcester, Vaillant) extend to 10 or even 12 years if you have the boiler serviced annually by an approved installer. The annual service is £85–£110, but you protect a part-replacement cost that could run into the thousands later. We add the boiler to our reminder system and book your service at the same anniversary date every year unless you opt out.
9. What we include in our installed price
Every South East HVAC quote includes:
- The boiler, complete with manufacturer warranty registered on your behalf
- Magnetic system filter (MagnaClean Pro 2 or equivalent)
- Chemical inhibitor and system flush
- New TRVs on all radiators (unless already smart-controlled)
- Smart thermostat or compatible programmer where the existing one is end-of-life
- Gas Safe Building Notice lodged with the register
- Disposal of the old boiler under WEEE
- 2-year workmanship warranty on top of the manufacturer warranty
10. Want a real Kent price?
A 15-minute site survey gives you a fixed written quote, itemised. Free across our core Kent coverage area — Sevenoaks, Sundridge, Tonbridge, Westerham, Bromley, Orpington, Dartford, Maidstone and surrounding postcodes. No call-back from a sales team, no pressure; the engineer who quotes is the engineer who fits.