Boiler Replacement Calculator
Estimate boiler replacement costs in the UK. Compare combi, system and heat pump options with installation costs, grants and running costs.
Boiler / Heating System Type
Boiler Brand Tier
Additional Options
Your Results
Estimated Total Cost
£1,800 – £2,780
Cost Breakdown
Boiler Cost
£990
to £1,540
Installation
£660
to £990
System Flush
£150
to £250
Flue Relocation
—
Not required
Estimated Running Costs
~£900–£1,200/year (gas tariff)
Expected Lifespan
10–15 years
All gas boiler installations must be carried out by a Gas Safe registered engineer, who must issue a Benchmark commissioning certificate on completion to validate the manufacturer warranty.
Tips for getting the best boiler replacement price
- Get at least three quotes from Gas Safe registered engineers — prices can vary by 30–40%.
- A like-for-like combi swap (same location, same flue position) is the cheapest option.
- Replacing in spring or autumn is typically cheaper than mid-winter emergency replacements.
- Ask if a magnetic filter is included — it protects the new boiler and is usually required for warranty.
- Check that the Benchmark commissioning document is completed and left with you after installation.
Frequently Asked Questions
How much does it cost to replace a boiler in the UK in 2026?+
Replacing a gas combi boiler in the UK in 2026 typically costs £1,500–£3,500 in total, including the boiler unit and installation. A budget combi boiler (e.g. Ideal or Potterton) with straightforward installation starts around £1,100–£1,700, while a premium Worcester Bosch or Viessmann with full system flush can reach £3,000–£4,500 for a large home. Oil boilers cost more, starting around £2,000 and reaching £4,000+ for premium units. Heat pumps are significantly more expensive but attract a £7,500 government grant via the Boiler Upgrade Scheme.
What is the Boiler Upgrade Scheme (BUS) grant and how do I apply?+
The Boiler Upgrade Scheme (BUS) is a UK government grant that provides £7,500 towards the cost of installing an air source or ground source heat pump. The grant is applied directly by your MCS-certified installer — you don't need to apply yourself. To be eligible, your property must be in England or Wales, have a valid EPC with no outstanding recommendations for insulation improvements, and the system must be installed by an MCS-accredited heating engineer. The grant was £7,500 for heat pumps as of 2024 and remains at this level for 2026.
Do I need a Gas Safe registered engineer to replace my boiler?+
Yes — it is a legal requirement in the UK that all gas boiler installations and replacements are carried out by a Gas Safe registered engineer. It is illegal for anyone who is not Gas Safe registered to work on gas appliances. After installation, the engineer must issue a Benchmark commissioning certificate, which also validates the manufacturer's warranty. You can verify any engineer's Gas Safe registration at gassaferegister.co.uk. Oil boilers must be installed by an OFTEC-registered technician.
Is a system flush necessary when replacing a boiler?+
A powerflush or magnetic filter clean is strongly recommended — and sometimes required by manufacturers to validate the warranty — when replacing a boiler on an older system. Central heating sludge, rust particles, and scale can damage a new boiler's heat exchanger within months. A full powerflush costs £300–£600 and takes half a day; a magnetic filter and chemical inhibitor dose (the minimum) costs £150–£250. Skipping the flush can void your boiler warranty and lead to costly repairs within 2–3 years.
How long does a boiler replacement take?+
A like-for-like combi boiler swap typically takes 1–2 days. If the flue needs relocating, pipework rerouting, or the system type is changing (e.g. from a back boiler to a combi), allow 2–3 days. A full heat pump installation is more involved and usually takes 2–5 days depending on the property and whether new radiators or underfloor heating is required. Gas Safe engineers must also complete Benchmark commissioning paperwork on the day of installation.