Boiler replacement cost calculator
A boiler quote is really three quotes — the appliance, the installation, and the state of the system it is joining. Price all three.
Last updated July 2026 · built by working UK builders
Only a Gas Safe registered engineer may work on gas. Check the card and the registration number on the Gas Safe Register — not just a logo on a van.
The install must be notified to Gas Safe within 30 days. You should receive a Building Regulations Compliance Certificate in the post.
The rates behind this calculator
All figures are 2026 UK prices for a competent, insured, VAT-registered contractor. Costs are shown as ranges because building work is delivered in ranges. A “×” value multiplies the whole build cost.
What are you doing?
| Option | Cost | Effect on total |
|---|---|---|
|
Like-for-like combi swap
Same position, same pipework |
£2,000–£3,400 | Added |
|
Combi swap and relocate
New position — new gas run, flue and condensate |
£2,800–£4,800 | Added |
|
Convert conventional system to a combi
Removing tanks and cylinder, capping the loft |
£3,200–£5,500 | Added |
|
System boiler with unvented cylinder
Right choice for 2+ bathrooms |
£3,800–£6,800 | Added |
|
Air source heat pump
Before the Boiler Upgrade Scheme grant |
£10,000–£16,000 | Added |
Boiler make
| Option | Cost | Effect on total |
|---|---|---|
|
Budget
Ideal, Baxi, Alpha |
— | ×0.88 |
|
Mainstream
Worcester, Vaillant |
— | ×1 |
|
Premium
Viessmann, top-tier Vaillant |
— | ×1.14 |
System work
| Option | Cost | Effect on total |
|---|---|---|
|
Powerflush or chemical clean
Non-negotiable on an old system |
£350–£800 | Added |
| Magnetic system filter | £120–£260 | Added |
| Smart thermostat and controls | £200–£550 | Added |
| TRVs on every radiator | £200–£600 | Added |
| Replacing radiators throughout | £1,800–£5,000 | Added |
| Replacing old microbore or steel pipework | £1,500–£5,000 | Added |
| Upsized gas supply pipe from the meter | £400–£1,200 | Added |
| Vertical flue or long horizontal run | £250–£700 | Added |
| Scaffold or access tower for the flue | £300–£900 | Added |
Where is the property?
Labour rates and builder demand vary more than materials do.
| Option | Cost | Effect on total |
|---|---|---|
| London | — | ×1.25 |
| South East | — | ×1.12 |
| South West | — | ×1.03 |
| East of England | — | ×1.03 |
| Midlands | — | ×0.97 |
| North of England | — | ×0.92 |
| Wales | — | ×0.92 |
| Scotland | — | ×0.95 |
| Northern Ireland | — | ×0.85 |
Applied to every total
| Item | Amount |
|---|---|
| Contingency | 6% of build cost |
| VAT | Included at 20% unless stated |
Choosing the right type
Combi
Heats water on demand. No cylinder, no loft tanks, so it frees up a cupboard and an airing space. Fine for one bathroom. Struggles with two simultaneous outlets, and flow rate depends on the incoming mains, which is why the same boiler performs differently street to street.
System boiler with unvented cylinder
Stores hot water at mains pressure. Handles two or three bathrooms comfortably. Needs cupboard space, an annual check on the expansion vessel and a G3 qualified installer. This is the right answer for most family houses with an en-suite.
Conventional (heat only)
Cylinder plus loft tanks. Mostly being replaced rather than installed, but it remains a sound choice for older properties with fragile pipework that would not enjoy mains pressure.
Air source heat pump
£10,000–£16,000 before the Boiler Upgrade Scheme grant, which reduces it substantially. Works best in a well-insulated house with larger radiators or underfloor heating and a proper heat loss calculation — not as a straight swap into an uninsulated Victorian terrace with the existing rads.
What separates a good install from a cheap one
- A heat loss calculation, not a boiler sized by guesswork. Oversizing is the norm and it costs you money every day.
- A cleaned system and a magnetic filter fitted on the return.
- Correct gas pipe size from the meter — an undersized run starves the boiler and shows up as lockouts in cold weather.
- Condensate run to a proper drain, internally where possible. External condensate pipes freeze and are the number one cause of boiler failure in a cold snap.
- Controls that actually control — room thermostat, TRVs and weather compensation if the boiler supports it.
Buying a house: what to check about the heating
Ask for the boiler's age, the last service record and the Gas Safe certificate for the install. Look for the benchmark book. Check whether radiators are cold at the bottom (sludge) and whether the system holds pressure. A RICS survey will note the boiler's presence and age but will not test it — that is a specific, separate job and worth doing on any purchase where the boiler looks over ten years old.
Frequently asked questions
How much does a new boiler cost in 2026?
A like-for-like combi replacement in the same position typically costs £2,000–£3,400 fitted. Relocating it adds £800–£1,400. Converting a conventional system to a combi runs £3,200–£5,500, and a system boiler with an unvented cylinder £3,800–£6,800.
Combi or system boiler?
A combi suits homes with one bathroom and modest simultaneous demand — no cylinder, no tanks, hot water on demand. Two or more bathrooms usually want a system boiler with an unvented cylinder, because a combi cannot serve two showers at once. Adding an en-suite to a combi house without upgrading the hot water is one of the most common renovation regrets.
Do I need a powerflush?
On any system more than about ten years old, yes. Manufacturers make the warranty conditional on the system being cleaned to their standard, and installing a new boiler onto a system full of magnetite sludge is the fastest way to block the heat exchanger. Budget £350–£800, and fit a magnetic filter afterwards.
How long does a boiler last?
Twelve to fifteen years for a well-serviced mainstream combi, sometimes twenty. Once a boiler is past twelve and needs a part that costs several hundred pounds, replacement usually makes more sense than repair — but a working boiler with a good service history is not an emergency just because it is old.
What paperwork should I receive?
A Gas Safe Building Regulations Compliance Certificate — the installer notifies Gas Safe within 30 days and the certificate is posted to you. Plus the benchmark commissioning checklist in the boiler manual, filled in and signed. Without both, the manufacturer’s warranty can be refused.
See what the advice looks like
Same builder, same £59, whichever stage you are at. Every one of these is a full worked example.
- Planning the jobIs it realistic, what should it cost, what consents does it need?
- Quotes in handA builder’s quote read line by line — what is missing and what to ask.
- Something has changed mid-jobA £9,400 variation, item by item: genuine extra or should have been priced?
- Arguing about qualityWhich complaints are real defects and which are normal tolerances.