Boiler quotes are a strange document to compare, because the same job can arrive priced anywhere from £1,800 to £6,000 depending on what's actually included. Fitted in 2026, a straightforward like-for-like gas boiler replacement — same type, same spot, same fuel — typically runs £1,800–£4,500, with £2,000–£3,000 the common range for a combi swap in an ordinary semi or terrace. Anything that changes the shape of the job — converting from an old back boiler, swapping from a heat-only boiler with a cylinder to a combi, or moving the boiler to a new room — pushes the number up toward £4,000–£7,000, sometimes more.
What moves the price within those bands is mostly mechanical: the boiler's output, how much pipework and flue has to change, and whether a cylinder or tank needs removing. What's worth more scrutiny than the headline figure is whether you're being sold more boiler than you need, or steered toward a full system change when a straight swap would do — and whether a heat pump genuinely belongs in the conversation instead, rather than being dismissed or oversold by whoever's quoting.
I assess buildings and heating systems for a living; I don't install boilers or heat pumps, so there's no unit sat in a van waiting to be sold. This is a straight read on what a new boiler costs in 2026, what actually drives that number, and an honest comparison with the heat pump alternative.
The short answer
Figures below were checked on 23 July 2026 against current Checkatrade, MyBuilder, Heatable and iHeat cost guides, cross-referenced with Energy Saving Trust replacement-cost data and UK government retrofit cost assumptions. As with most trades, the South East and London tend to sit toward the upper end of these ranges.
| Job | Typical fitted cost | What's involved |
|---|---|---|
| Like-for-like combi swap | £1,800–£3,500 | Same boiler type, same location, new flue and controls |
| System or regular boiler, with a cylinder | £2,200–£4,500 | Cylinder work, extra pipework, one to two days' labour |
| Change of boiler type, moved location, or back-boiler removal | £4,000–£7,000+ | New pipe runs, flue relocation, tank/cylinder removal, two to three days |
| Oil boiler (off gas grid) | £3,500–£5,500 | Includes tank and flue work; heat pump often the honest alternative here |
Most quotes break down roughly the same way: the boiler unit itself is £600–£3,600 depending on output and brand, and labour adds a further £600–£1,500, with a Gas Safe registered engineer typically charging £300–£600 a day. A like-for-like combi swap is usually a single day's work; anything involving a new flue route, a relocated boiler, or a back-boiler conversion runs to two or three days once the extra pipework, making good, and possibly a new cylinder are added in.
What drives the price
Boiler type and output. A combi boiler sized to an ordinary semi with one bathroom sits toward the bottom of the range; a larger combi built to serve two bathrooms simultaneously, or a system boiler paired with a bigger cylinder for a house with more people in it, costs more before a spanner is picked up.
Whether it's a straight swap or a change of system. This is the single biggest lever. Replacing a combi with a combi in the same spot is quick and predictable. Converting an old back boiler to a combi, or moving the boiler from an airing cupboard to a kitchen, means new pipe runs, a new flue position, and often removing redundant tanks or a cylinder — work that can add £1,500–£3,000 to an otherwise ordinary job.
Fuel type. Gas remains the cheapest to install for most homes still on the grid. Oil boilers cost more, largely because of tank and flue work, and are increasingly a case where an honest quote should at least raise the heat pump alternative, since an oil-fired household typically qualifies for the higher £9,000 Boiler Upgrade Scheme grant rather than the standard £7,500.
Brand and warranty length. A budget boiler with a 2-year warranty and a mid-range one with a 10-12 year manufacturer warranty can differ by several hundred pounds up front — usually worth it, since labour on a warranty repair is normally covered as well as parts.
VAT. A standard gas, oil or LPG boiler installation is charged at the full 20% VAT rate. This is a genuine point of contrast with a heat pump or biomass boiler, both of which currently qualify for 0% VAT under the energy-saving materials relief — worth factoring in if you're weighing the two side by side, since it's rarely spelled out on a like-for-like quote comparison.
Location. As with most trades, London and the South East carry a premium over the national average, for the usual reasons of overheads and demand.
Boiler vs heat pump, honestly compared
This is the comparison most boiler quotes don't raise, because whoever's quoting is usually only set up to sell one of the two. Upfront, a boiler wins clearly: a like-for-like gas swap at £1,800–£4,500 sits well below a heat pump's £9,000–£16,000 installed cost, even after the £7,500 Boiler Upgrade Scheme grant brings that down to roughly £1,500–£8,500.
Running costs are closer than either camp tends to admit. At current price cap rates, a modern condensing gas boiler and a well-installed heat pump on a standard electricity tariff land within a similar range annually — sometimes gas slightly ahead, sometimes the heat pump, depending on the property's insulation and the heat pump's actual seasonal performance. The gap widens meaningfully in the heat pump's favour on a dedicated heat-pump or off-peak electricity tariff, and narrows or reverses on a standard variable tariff with a poorly commissioned system. Lifespan cuts the other way: a gas boiler typically lasts 10-15 years against 20-25 for a heat pump, so the heat pump's higher upfront cost is being spread over a genuinely longer replacement cycle.
My honest read: if your gas boiler has failed or is on its last legs and you need heat back on this week, a straight swap is the sensible, unglamorous answer, and there's no shame in it. If you've got time to plan and your home has decent fabric — reasonable insulation, no major damp or ventilation issues to sort first — a heat pump is a genuinely comparable long-term proposition, not just a subsidised gesture. What I'd resist is either extreme: replacing gas with gas purely out of habit when the grant and the fabric both stack up for a heat pump, or being sold a heat pump into a solid-wall house with single glazing and no heat loss survey behind the quote.
Repair or replace? The signs I look for
A boiler repair typically costs £120–£750, averaging around £300 for a straightforward fault like a diverter valve, fan, or circuit board. Below that, repair usually makes sense. The maths tips toward replacement when a boiler is past 10-12 years old and needs its second or third repair inside a couple of years, when parts are getting genuinely hard to source, or when efficiency has visibly dropped — an old boiler running at 60-70% efficiency against 90%+ for a modern condensing unit is quietly costing more in gas than the repair bill suggests. I'd also replace on safety grounds without much debate: any sign of a flue gas or carbon monoxide problem, confirmed by a Gas Safe engineer, ends the conversation about repairing.
What I'd watch for in a quote
- A Gas Safe registration checked directly, not just claimed on a business card — the online register takes thirty seconds and roughly one in five gas jobs inspected after unregistered work turns up an active safety risk.
- The right boiler size, not the biggest one on the van. An oversized boiler short-cycles and runs less efficiently; ask what the sizing was based on.
- VAT and extras itemised — flue kit, magnetic filter, chemical power flush, and any gas pipe upgrade should be on the quote, not added after the job's started.
- Warranty length and who backs it — a manufacturer-backed 10-12 year warranty beats a reseller's short one, and matters more than a small difference in headline price.
- A genuine like-for-like comparison if you're also weighing a heat pump — ask for both quotes from someone with no preference either way, not from an installer who only fits one of the two.
Questions I get asked
Can I get a free or grant-funded boiler? Only if you qualify for ECO4, which funds free or heavily subsidised boiler replacements for households on qualifying benefits, or via a council's local flexible eligibility route, typically tied to an EPC rating of D or below. It isn't a general grant like the Boiler Upgrade Scheme for heat pumps — most homeowners replacing a boiler pay the market rate in full, and ECO4 itself is due to close at the end of 2026 with no confirmed replacement yet.
How long does a boiler installation take? A straightforward like-for-like combi swap usually takes one day. Moving the boiler's location, converting from a back boiler, or changing boiler type typically takes two to three days, since it involves new pipework, a new flue run, and sometimes removing an old cylinder or tank.
Do I need a bigger boiler for a bigger house? Not necessarily in kW output — a combi boiler is sized to your hot water demand, how many bathrooms it needs to serve at once, more than raw floor area. A larger, older house on a system or regular boiler is more likely to need a bigger cylinder than a bigger boiler. An oversized boiler short-cycles and runs less efficiently, so bigger is not automatically better.
Is it worth paying more for a longer warranty? Often, yes, provided it comes from the manufacturer rather than a reseller add-on, and provided the installer is accredited to offer it. A 10-12 year manufacturer warranty on a mid-range boiler is usually better value than the cheapest unit with a 2-year warranty, since labour on a warranty repair is normally covered too — the parts are rarely the expensive part of a repair.
If you're weighing up a straight boiler swap against a heat pump, or want an honest read on whether your home's fabric and ventilation are ready for either before you commit to a quote, that's exactly the kind of question a PAS 2035 retrofit assessment is built to answer — heat loss, fabric, and the right sequencing of work, from someone with nothing to sell you afterwards. It often pairs well with an up-to-date EPC if a mortgage, sale or MEES compliance is also in the mix. Call 07946 618203 or get in touch and I'll give you a straight answer on where to start.
Small print. This guide is general information, not advice on a specific property, and it doesn't replace a proper quote and, where relevant, a heat loss survey for your home. Prices were researched and correct to the best of my knowledge on 23 July 2026; costs, grants and VAT rules move and vary by region and property. Always get at least three written quotes before instructing.