The cost of a new boiler depends far more on the installation than on the boiler itself: whether you keep the same type of boiler in the same place, how the flue, gas pipe and condensate need to run, and what condition your heating system is in. A like-for-like combi swap in the same spot is the simplest job, while changing boiler type, moving the boiler or upgrading the gas supply all add labour and materials.

Why two quotes for the same boiler can look so different

Two installers can quote very differently for what looks like the same boiler. Usually one of them has priced the whole job properly and the other has left things out, or one has spotted work the other missed. The boiler is only part of the price. The rest is the flue, the gas and water connections, the condensate pipe, the controls, cleaning the system, removing the old boiler and the time it all takes to do safely and to the manufacturer’s instructions.

The quickest way to see a price for your home is our online boiler quote tool, which asks about your current boiler, where it is and what you need, then gives a fixed price in a couple of minutes.

The factors that affect the cost of a new boiler

1. The type of boiler

There are three main types. A combi boiler heats water on demand and needs no tanks. A system boiler heats a hot water cylinder and suits homes with more than one bathroom used at once. A regular (heat only) boiler works with a cylinder and cold water tanks in the loft. Combis are generally the simplest to install. System and regular boilers involve a cylinder and more controls. Our guide to the best combi boilers explains when a combi is the right choice and when it is not.

2. Changing from one type to another

Swapping a boiler for the same type is the least disruptive job. Converting a regular system to a combi means removing the cylinder and loft tanks, capping old pipework, rerouting hot and cold supplies and often changing controls. It takes longer and costs more, but it can free up the airing cupboard and the loft. Changing a combi to a system boiler means adding a cylinder, which adds cost the other way.

3. Boiler size and hot water demand

For a combi, the output figure mainly decides how quickly hot water comes out of the taps. A small flat and a four bedroom house with two showers need very different boilers. A good installer sizes the boiler to your home, your water pressure and flow rate, and how many outlets you use at once. A bigger boiler than you need costs more and can cycle on and off more, which wastes gas.

4. Brand, model and guarantee

Boiler ranges differ in build quality, features and guarantee length. Manufacturers often offer longer guarantees on their better ranges when fitted by an accredited installer. We are an Ideal Max accredited installer and a Vaillant myREWARDS installer, and we can offer manufacturer guarantees of up to 12 years on selected Ideal boilers and up to 10 years on selected Vaillant boilers. A longer guarantee usually means a slightly higher price but fewer surprises later.

5. Moving the boiler

Keeping the boiler where it is avoids new gas, water, heating, condensate and electrical runs. Moving it, for example from a kitchen wall into a loft or cupboard, means extending all of those and fitting a new flue. The further it moves, the more work there is. A loft boiler also needs safe access, which manufacturers normally expect to include a fixed ladder, lighting and a boarded route to the boiler.

6. The flue

A horizontal flue straight out through the wall behind the boiler is the simplest. Vertical flues through the roof, long flue runs, flue extensions and plume kits to steer the vapour away from windows or a neighbour’s property all add parts and time. Flue positions must meet the manufacturer’s clearances from windows, doors, boundaries and gutters, and sometimes that forces a longer route.

7. The gas supply pipe

A modern combi can need more gas at full output than an old boiler. If the gas pipe from the meter is too small for the new boiler, it has to be upgraded so the boiler gets enough gas to run safely and efficiently. Your engineer checks this on the survey. It is one of the most common items missing from cheap quotes.

8. The condensate pipe

Every condensing boiler produces acidic water that must drain away. An internal run to a waste pipe is best. If the pipe has to go outside, it should be a larger diameter and insulated so it does not freeze in winter. A frozen condensate pipe is one of the most common winter breakdowns, so the route is worth getting right at installation.

9. The condition of your heating system

Old systems collect sludge and scale. Boiler manufacturers expect the system to be cleaned before a new boiler goes on, followed by inhibitor, and a magnetic filter to catch debris from then on. Most systems need a chemical clean. Heavily sludged systems may need a powerflush, which takes longer. Skipping the clean is a false economy because debris damages a new boiler’s heat exchanger and pump.

10. Controls

In England, the Boiler Plus standard means every new gas boiler needs a timer and a room thermostat, and a new combi also needs an extra energy saving measure such as weather compensation, load compensation or a smart thermostat with automation and optimisation. A basic programmable thermostat costs less than a smart one, but the upgrade can pay back in comfort and lower gas use.

11. Anything else the survey finds

Some jobs uncover extra work: radiators that are undersized or failing, valves that will not close, pipework that needs changing, or an electrical supply without a proper fused spur. Older boilers, flues and cupboard linings can contain asbestos. If an engineer suspects it, it must be tested before it is disturbed.

Quick guide: what pushes the price up or down

Factor	Keeps the cost lower	Pushes the cost higher
Boiler type	Combi for combi swap	Regular to combi conversion, or adding a cylinder
Location	Same position	Moving rooms or into the loft
Flue	Short horizontal flue	Vertical flue, long runs, plume kit
Gas pipe	Existing pipe adequate	Pipe upgrade from the meter
Condensate	Short internal run	Long external run needing protection
System condition	Clean system, chemical clean	Heavy sludge needing a powerflush
Controls	Standard programmable thermostat	Smart, zoned or compensating controls

What a proper quote should include

Before you compare prices, check each quote covers the same work:

• The exact boiler make, model and output
• Flue type and route
• Gas pipe check and any upgrade needed
• Condensate route
• System clean and inhibitor, and a magnetic system filter
• Controls that meet Boiler Plus
• Removal and disposal of the old boiler
• Building regulations notification through Gas Safe, and registration of the guarantee with the manufacturer
• Who will do the work and how long it will take

Our new boiler packages include a magnetic system filter, the first year’s service and removal of the old boiler.

Repair or replace first?

Not every old boiler needs replacing. If yours is under ten years old, has had regular services and the fault is a single part, a repair is often the sensible choice. If it is older, breaking down repeatedly, or parts are hard to get, replacement usually makes more sense. Our honest repair or replace guide goes through the decision in more detail.

How we price it

Installations are quoted as a fixed price after a free survey, so the price you agree is the price you pay. You can get your price online in a couple of minutes with our boiler quote tool, and we confirm it on the survey. Our other rates, including repairs and servicing, are published on our prices page.

Frequently asked questions

Is it cheaper to replace a combi with another combi?

Usually, yes. A like-for-like combi swap in the same position reuses most of the existing connections, so it is the quickest and simplest installation. The final price still depends on the flue, gas pipe and the condition of your system.

Does moving the boiler add a lot to the cost?

It depends how far it moves. Moving it within the same room may only need a little extra pipework, but moving it to another room or the loft means new gas, water, condensate and electrical runs and a new flue.

How long does a new boiler installation take?

A straightforward combi swap is normally done in a day. A conversion from a tank-fed system to a combi, or a move to a new location, usually takes two days or more depending on the pipework involved.

Do I need a powerflush with a new boiler?

Not always. Every system needs cleaning before a new boiler goes on, but most only need a chemical clean. A powerflush is recommended when the system is heavily sludged, for example when radiators are cold at the bottom or the water is black.

Why do online boiler prices vary so much?

Some headline prices cover only the most basic swap and add extras later. Compare what is included, the boiler model, the guarantee length and who does the work, rather than the first number you see.

New boiler installation across Hertfordshire, Bedfordshire and Cambridgeshire

If your boiler is getting old or breaking down, our Gas Safe engineers can survey your home and give you a fixed price with no hidden extras. Start with our boiler installation page or call 01462 506374, answered 24 hours a day, 7 days a week.