When your boiler starts breaking down every winter, the question quickly becomes whether to keep paying for repairs or invest in a new boiler. In the UK, a straightforward combi boiler replacement typically costs £2,000 to £3,500 fitted, while system and conventional boiler replacements, or conversions from one type to another, usually range from £2,500 to £5,500 depending on the work involved.
The right choice depends on the size of your home, how many bathrooms you have, your water pressure and whether you want to stay on gas or move to a low-carbon alternative. A modern condensing boiler is far more efficient than one fitted 15 or 20 years ago, so a well-planned boiler upgrade can lower your heating bills as well as end the cycle of call-outs and cold showers.
This guide covers new boiler prices by type, when repairing is better than replacing, what a fair quote should include, the Gas Safe and building regulation rules, the grants and finance worth knowing about, and exactly what to expect on installation day.
Boiler replacement prices at a glance
| Type of job | Typical cost fitted | Best for |
| Combi swap (same position) | £2,000–£3,500 | Flats and 1–3 bed homes, one bathroom |
| System boiler replacement | £2,200–£4,500 | Larger homes, two or more bathrooms |
| Conventional (regular) boiler | £2,000–£4,500 | Older homes with tanks in the loft |
| Conversion to a combi | £3,000–£5,500 | Freeing up loft and cupboard space |
| Back boiler removal | £3,500–£6,000 | Old fireplace back boilers |
| Oil boiler replacement | £2,500–£5,500 | Homes off the gas grid |
Prices include the boiler, flue, standard controls, a system flush and labour. Moving the boiler to a new room, upgrading the gas pipe or replacing radiators will add to the total.
Which type of boiler do you need?
- Combi boiler: heats water instantly from the mains, so there is no hot water cylinder or loft tank. Compact and efficient, but can struggle if two showers run at once.
- System boiler: stores hot water in a cylinder, usually in an airing cupboard. Supplies several taps and showers at the same time, making it a good fit for family homes with more than one bathroom.
- Conventional (heat-only) boiler: uses a cylinder plus cold water and expansion tanks in the loft. Often kept in older properties where the pipework was designed for it or mains pressure is low.
Size matters too. An installer should match the boiler output (in kW) to your home’s heating and hot water demand rather than simply fitting the biggest model. An oversized boiler costs more to buy and can run less efficiently.
Repair or replace?
- the boiler is under 10 years old
- it is a one-off fault with an easily sourced part
- it is still under warranty
- it is 15 years old or more
- breakdowns happen every year
- parts are discontinued or repairs exceed a third of a new boiler’s cost
- it is a non-condensing model
If your boiler has failed completely in winter, ask for a temporary fix while you get proper quotes – rushed replacements are where most homeowners overpay.
What a fair quote should include
Ask at least three Gas Safe registered engineers to quote, and check that each one lists:
- the boiler make, model and output, and the length of the manufacturer’s warranty;
- a system flush (powerflush or chemical flush) and a magnetic filter, which most manufacturers require to honour the warranty;
- the controls – thermostat, programmer or smart control – and any energy-saving device needed to meet building regulations;
- flue, condensate pipe and any gas pipe upgrades;
- removal and disposal of the old boiler and tanks;
- building regulations notification and registration of the warranty.
Long warranties of 7, 10 or even 12 years are common on mid-range and premium boilers, but they usually depend on an annual service by a Gas Safe engineer. Factor that yearly cost into your decision.
The rules: Gas Safe and building regulations
By law, any work on a gas boiler must be carried out by an engineer on the Gas Safe Register. Every registered engineer carries an ID card showing the types of gas work they are qualified for, so check it covers domestic boilers. Oil boilers should be fitted by an OFTEC-registered technician.
A boiler replacement is notifiable building work. Your engineer registers it through their competent person scheme, and you should later receive a Building Regulations Compliance Certificate – keep it, as you will need it when you sell your home. In England, new gas boilers must also meet minimum efficiency and controls standards, which a reputable installer will build into the quote.
Grants, finance and low-carbon alternatives
There is no general grant for a like-for-like gas boiler, but a few routes can reduce the cost:
- Boiler Upgrade Scheme: in England and Wales, switching from a gas, oil or LPG boiler to a heat pump can attract a grant of £7,500. Read our full guide to heat pump installation, grants and running costs.
- Warm Homes: Local Grant: low-income households in England with a less efficient home may qualify for funded heating and insulation upgrades through their council.
- Council and devolved schemes: Scotland, Wales and Northern Ireland have their own heating support, and some councils offer help for older or vulnerable residents.
- Finance: many installers offer monthly payment plans. Compare the APR and total amount repayable, not just the monthly figure.
What to expect on installation day
⏱ Combi swap: usually one day. Your heating and hot water will be off for most of it.
⏱ Conversion or relocation: typically two to three days, as tanks are removed and pipework rerouted.
🔧 The work: the old boiler is drained and removed, the system flushed, the new boiler, flue and controls fitted, then the system refilled and tested.
📋 Handover: the engineer should show you the controls, complete the Benchmark checklist in the manual and register your warranty.
Clear the area around the boiler and the route to it before the engineer arrives, and make sure there is access to the loft if tanks are being removed.
Frequently asked questions
How long does a boiler last?
Most modern boilers last 10–15 years with annual servicing. Many keep running longer, but efficiency drops and parts become harder to find.
Can I still install a new gas boiler?
Yes. Homeowners can replace an existing gas boiler with a new one. Rules on heating in brand-new homes are changing, so new builds are increasingly fitted with low-carbon systems instead.
How much could a new boiler save on my bills?
Savings depend on how old and inefficient your current boiler is. Replacing an old non-condensing model with an efficient condensing boiler and good controls can make a noticeable difference to gas bills.
Do I need to replace my radiators?
Not usually for a gas boiler swap. A system flush is normally enough, though very old or damaged radiators may be worth replacing at the same time.
How can I check an engineer is registered?
Ask to see their Gas Safe ID card and check the licence number on the Gas Safe Register website, or call the register directly.
Prices reflect typical UK installer quotes; rules based on Gas Safe Register and GOV.UK guidance.
Independent guide – not linked to any boiler brand or installer.
