New Boiler Cost In Kent 2026: Combi, System And Oil Installs Explained

By Lucas Morley, owner and heating engineer at Evo Flow Heating (Heat Geek partner, Gas Safe registered) · About Evo Flow Heating · Last updated 19 July 2026

Almost every conversation about a new boiler starts the same way. Something has failed, or the repair bills have started stacking up, and the first thing anyone wants to know is what it is going to cost. That is a fair question and this guide answers it properly, with the real ranges we quote across Kent rather than a national average that bears no relation to your house.

But there is a second question hiding underneath it, and it matters more than the first: what are you actually paying for? Two quotes for the same house can sit £1,500 apart and both be honest. The difference is usually in the work nobody photographs, which is the pipework, the controls, the system cleanse and the sizing calculation. This guide covers both questions.

How Much Does A New Boiler Cost In Kent In 2026?

Here are the ranges we work to across Kent. These are fully installed prices including the boiler, labour, a system cleanse, new controls and warranty registration, not a boiler-only price with the fitting added later.

Job type	Typical installed cost	Usual timescale
Like-for-like combi swap	£2,000 to £3,200	1 day
Combi swap plus boiler relocation	£2,800 to £3,800	1 to 2 days
Regular or system boiler, cylinder retained	£2,600 to £3,600	1 to 2 days
System boiler with new unvented cylinder	£4,000 to £6,500	2 to 3 days
Conversion from regular to combi	£3,200 to £4,500	2 days
Back boiler removal and full replacement	£3,500 to £5,000	2 to 3 days
Oil boiler replacement (rural Kent)	£3,500 to £5,500	1 to 2 days

Those ranges are wide on purpose, because the spread is real. A straight swap in a house where the pipework is sound sits at the bottom. The same boiler in a house where the gas supply needs upgrading, the flue route has to change, or thirty years of sludge has to come out of the system first will sit near the top. An honest installer will tell you which one you are before quoting, and a written itemised quote makes it obvious.

What Actually Moves The Price

• Moving the boiler. Relocating from a bedroom cupboard to the kitchen means new gas, water, condensate and flue runs. Usually the single biggest line on a quote after the boiler.
• Gas supply size. Older properties often have 15mm gas pipe where a modern boiler needs 22mm. Not optional, and not always visible until someone looks.
• Flue routing. A straight flue through an external wall is simple. A vertical flue through a roof, or one that has to clear a boundary or an opening window, is not.
• System condition. A sludged system needs a powerflush or at minimum a chemical cleanse before a new boiler goes on, and every major manufacturer requires it for the warranty to stand.
• Controls. A basic on/off programmer costs very little. Weather compensation and proper zoning cost more and save money every year afterwards.
• Cylinder work. Unvented cylinders need G3 qualified installation and the discharge pipework done properly, which is the part that gets bodged most often.

Combi Boiler Cost: The Most Common Kent Installation

A combi heats your hot water on demand and needs no cylinder, which is why it suits the majority of two and three bedroom homes across Dartford, Gravesend and Maidstone. A like-for-like replacement typically runs £2,000 to £3,200 fully installed.

The catch with a combi is flow rate. It can only heat water as fast as your mains can deliver it, so before recommending one we measure the incoming flow at the kitchen tap. If your mains delivers 12 litres a minute, a combi rated for 16 litres a minute will never achieve that figure no matter what the brochure says. In parts of Kent with older mains connections this is the deciding factor, and it is a ten minute test that a surprising number of quotes skip.

A combi is usually the wrong answer if you have two bathrooms in regular simultaneous use, if your mains flow is poor, or if the household genuinely runs several hot taps at once in the morning. In those houses a system boiler with a cylinder gives a better result even though it costs more up front. We cover both on our gas boiler installation service page.

System Boiler And Cylinder Cost For Larger Kent Homes

A system boiler heats a stored cylinder of hot water rather than heating it on demand. That means several bathrooms can run at once without the pressure collapsing, which is why it remains the right choice for the larger detached stock around Sevenoaks, Tonbridge and the Weald.

• System boiler, existing cylinder retained: £2,600 to £3,600
• System boiler with a new unvented cylinder: £4,000 to £6,500
• Add for relocating the cylinder (airing cupboard to loft or utility): £600 to £1,400

Cylinder sizing is where these jobs go right or wrong. It should follow your household’s actual hot water pattern, not the number of bedrooms, because bedrooms do not take showers. A 250 litre cylinder in a house of two people is a tank of water you pay to keep warm and never use. Kent is also a hard water area, which is hard on cylinder coils and expansion vessels, so it is worth designing around rather than discovering in year three.

Oil Boiler Replacement Cost In Rural Kent

Mains gas stops at the edge of a lot of Kent villages, which is why properties around Ide Hill, Underriver, Bough Beech and out through the Weald still run on kerosene. A new oil boiler typically costs £3,500 to £5,500 installed, with the spread driven by whether the boiler is internal or in an outbuilding, and whether the tank and fuel line need work at the same time.

Two things are worth adding to the sum before you commit. First, if the tank is more than about twenty years old or is single skin, allow for replacement while the site is already disturbed. Second, and more importantly, an off grid property is the strongest heat pump candidate in the county, because oil is the fuel a heat pump beats most comfortably on running cost, and the £7,500 Boiler Upgrade Scheme grant applies on the switch. Before spending £5,000 on another oil boiler it is worth seeing both numbers side by side. We quote either, and we will tell you plainly which one the maths favours for your property. Our oil boiler service page covers the work in more detail.

Why Two Quotes For The Same Boiler Differ By £1,500

This is the question we get asked most, usually by someone holding three quotes with a £1,500 spread and no idea how to read them. The boiler itself is rarely where the difference sits. Most of the gap lives in these lines:

Line item	Lower quote	Higher quote
System cleanse	Chemical flush, or nothing	Full powerflush plus water test
Boiler sizing	Matched to the old boiler	Heat loss calculation first
Controls	Basic on/off programmer	Weather compensation, zoning
Filter	Not included	Magnetic filter fitted
Pipework	Reused as found	Upgraded where undersized
Warranty	Standard 2 to 5 years	Registered 10 years

Neither column is dishonest. The lower quote is a boiler swap and the higher one is a heating system upgrade. What you should not accept is not knowing which you are buying. Ask for the quote itemised and the difference becomes obvious in about thirty seconds.

What Happens On Installation Day

A straight combi swap is a single day. Bigger jobs run to two or three. The shape is much the same either way:

1. Protection down first. Dust sheets on floors and worktops before anything is disconnected.
2. Old boiler drained and removed. Taken away and disposed of, not left in your garden.
3. System cleanse. Powerflush or chemical cleanse depending on what the water test showed at survey.
4. Pipework and gas supply. Upgraded where the survey identified it, before the new boiler goes on the wall.
5. New boiler fitted and flued. Mounted, connected, magnetic filter fitted on the return.
6. Fill, inhibit, pressure test. Corrosion inhibitor dosed and the water quality recorded on the Benchmark checklist.
7. Commissioning and balancing. Flow temperature set by design, radiators balanced, gas rate and combustion checked.
8. Handover. Controls explained in person, paperwork and warranty registration completed, site left clean.

That Benchmark checklist inside your boiler documentation matters more than it looks. It is the manufacturer’s evidence that the system was cleansed and treated properly, and if a heat exchanger fails in year six on a system that was never flushed, several brands will use its absence to challenge the claim.

Hidden Costs To Check Before You Sign

Most of the unpleasant surprises on a boiler job are not surprises to the installer. They are things that were visible at survey and simply were not mentioned. Before accepting any quote, ask directly whether each of these is included:

• Removal and disposal of the old boiler. It should be taken away, not left for you to deal with.
• Magnetic filter. Around £120 to £180 fitted, and several manufacturers now require one for the warranty. Lower quotes often leave it off.
• Gas supply upgrade. If your gas pipe is undersized, this is not optional work. Find out at quote stage, not on the day.
• Making good. Who fills the holes and repairs the plaster where the old flue came out?
• Warranty registration. A 10 year warranty only exists if someone actually registers it within the manufacturer’s window.
• Building control notification. Every gas boiler installation must be notified. Your Gas Safe registered installer does this, and you should receive the certificate.
• Scaffolding or access equipment for a vertical flue or an awkward roof termination.

None of these are unusual and none of them should be dramatic. The point is that a quote which includes all of them will look higher than one that quietly excludes half of them, and the second quote is not actually less expensive. It is just less complete.

Should You Repair Or Replace?

Not every boiler needs replacing, and we will say so when it does not. As a rough guide, replacement usually wins when two or more of these are true:

• The boiler is over 12 to 15 years old and efficiency has dropped noticeably
• A single repair would cost more than a third of a replacement
• Parts are becoming hard to source for the model
• It has needed more than one repair in the past two years
• It is a back boiler or a non-condensing unit
• Radiators are cold at the bottom and the system has never been cleansed

If only one applies, a repair is often the sensible answer and we will quote it. A £180 fault that buys another five years is a better outcome for you than a boiler you did not need, and we would rather do that job and be the people you call next time.

Frequently Asked Questions

How Much Does A New Boiler Cost In Kent?

A like-for-like combi swap is typically £2,000 to £3,200 installed. A system boiler with a new unvented cylinder runs £4,000 to £6,500, and an oil boiler replacement £3,500 to £5,500. All of ours are fixed written quotes given after a free survey, with no call-out fee.

How Long Does A New Boiler Installation Take?

Most like-for-like swaps are completed in a single day. Moving the boiler, converting from a regular system to a combi, or removing a back boiler will usually take two to three days.

What Size Boiler Do I Need?

For heating, most Kent three bedroom homes need between 6kW and 12kW, which is far less than the 24kW to 30kW commonly fitted. Combi boilers are rated on hot water flow rather than heating output, which is why the headline number looks large. The right answer comes from a room by room heat loss calculation, which we do before quoting rather than after.

Do I Need A Powerflush With A New Boiler?

The system has to be cleansed and treated to BS 7593 standards, and that is a warranty condition for every major manufacturer. Whether that means a full powerflush or a chemical cleanse depends on the state of your system water, which we test at survey stage rather than guessing.

Which Boiler Brands Do You Install?

Worcester Bosch, Vaillant and Ideal are our usual choices, with warranties of up to 10 years registered on your behalf. The brand matters far less than the sizing and the installation quality, and any competent engineer will tell you the same.

Is It Worth Getting A Heat Pump Instead?

For off grid properties on oil or LPG, very often yes, because the £7,500 grant applies and the running cost comparison is favourable. For a mains gas home it depends on the property and how well the system is designed. We quote both routes side by side with real numbers so you can decide on evidence.

If you are weighing up a new boiler anywhere across Kent, the useful first step is a proper heat loss calculation rather than another quote pulled off a rule of thumb. Lucas will survey the property, run the numbers, and give you a written itemised price. If a repair would serve you better, he will tell you that instead.