The Simple Rule
If your boiler is over 10 years old and the repair cost is more than £400, replacement is almost always more cost-effective. A new boiler comes with a 5–12 year warranty and 90%+ efficiency vs 65–80% for an aging unit.
Signs Your Boiler Needs Replacing
Urgent
Yellow or Orange Flame
A healthy gas flame is blue. A yellow flame indicates incomplete combustion and a potential carbon monoxide risk. Stop using the boiler and call a Gas Safe engineer immediately.
Age Over 12–15 Years
The average boiler lasts 12–15 years with annual servicing. Beyond this, repair frequency and costs increase sharply while efficiency declines.
Frequent Breakdowns
More than one repair in 2 years on an older boiler usually means replacement is more economical. At £300–£500 per call-out, costs add up quickly.
Rising Gas Bills
Declining efficiency shows in your bills before it shows in performance. A 15-year-old boiler may be 70–75% efficient vs 90%+ for a new model.
Kettling (Rumbling Noises)
A rumbling, banging, or boiling sound indicates limescale or sludge in the heat exchanger. Can sometimes be repaired with a power flush, but on older boilers often indicates replacement is needed.
Persistent Pressure Loss
A boiler that repeatedly loses pressure may have a failing pressure relief valve or a system leak. If recurring after repair, the boiler body may be failing.
New Boiler Costs
| Type | Typical Cost (Installed) | Max Warranty |
|---|---|---|
| Gas combi boiler (like-for-like swap) | £1,800 – £3,000 | 12 years (Worcester Bosch) |
| Gas system boiler + new cylinder | £2,000 – £3,500 | 12 years (Worcester Bosch) |
| Oil boiler replacement | £3,000 – £5,000 | 5–7 years |
| Air source heat pump (with £7,500 BUS grant) | £500 – £6,500 net | Up to 12 years |
The £7,500 BUS grant applies to all homeowners replacing any fossil fuel or electric heating with a heat pump — including mains gas, oil, and LPG. The scheme runs until March 2028. We advise on the right option during your free survey.
New Boiler Cost by Type & Size in Cornwall
Choosing the right new boiler is about matching the boiler type and output (kW) to your property. Here is what a fully installed boiler replacement typically costs in Cornwall in 2026, with the property type each is best suited to. All figures include the boiler, standard fittings, a system flush, a magnetic filter and Gas Safe (or OFTEC, for oil) certification.
| Boiler type & size | Indicative cost (installed) | Best for |
|---|---|---|
| Gas combi, 24–28kW | £1,800 – £2,600 | 1–2 bed flats & terraces, one bathroom (Camborne, Redruth) |
| Gas combi, 30–35kW | £2,200 – £3,000 | 3-bed semis with one bathroom & good mains pressure (Truro, Falmouth) |
| Gas system boiler + cylinder, 24–30kW | £2,400 – £3,500 | Larger 3–5 bed homes with two or more bathrooms (St Austell, Bodmin) |
| Oil combi / system, 18–35kW | £3,000 – £5,000 | Off-gas-grid rural homes keeping oil short-term (Penzance, rural parishes) |
| LPG combi / system, 24–35kW | £2,400 – £4,200 | Off-gas homes on bulk LPG (often better served by a heat pump — see below) |
| Air source heat pump (after £7,500 BUS grant) | £500 – £6,500 net | Any home, especially off-gas oil/LPG replacements wanting lower long-term costs |
Indicative installed prices for Cornwall in 2026 — your exact figure depends on the model, output, flue route, gas/oil supply and any system upgrades. We give a fixed, itemised quote after a free survey.
Before You Commit
Should You Switch to a Heat Pump Instead?
Before paying £3,000–£5,000 for a new oil or LPG boiler, it is worth doing the maths on an air source heat pump. With the £7,500 Boiler Upgrade Scheme grant deducted up front, a heat pump can land at a similar net cost to a new oil boiler — while running cheaper and qualifying for stable, capped electricity pricing rather than volatile oil and LPG.
- →Replacing oil or LPG? The case is strongest here. A heat pump beats oil running costs by roughly 15–20% and LPG by 40%+, and the £7,500 grant offsets most of the higher upfront cost.
- →Boiler is 12+ years old and on the way out? Replacing now rather than repairing means the grant offsets the capital while you would be paying for a new appliance anyway.
- →Have (or planning) solar PV? A heat pump can run partly on your own electricity, cutting running costs further.
- →Modern mains gas combi working fine? A like-for-like new gas boiler is often the pragmatic short-term choice — running costs are close, and a heat pump becomes more compelling at the boiler's natural end of life.
We are MCS-certified for heat pumps and Gas Safe registered for boilers, so we have no axe to grind either way — we will give you an honest side-by-side comparison during your free survey. Read the full £7,500 BUS grant guide or our heat pump vs gas boiler running-cost comparison.
Boiler Installation Areas
Boiler Replacement FAQs
01 How long does a new boiler installation take?
02 Which boiler brand has the longest warranty?
03 Is a heat pump better than a new boiler for an oil-heated home?
04 What is the difference between a combi and a system boiler?
05 Should I get a magnetic filter fitted with my new boiler?
Related Guides
Blog
When to Replace Your Boiler
Signs, costs, and when to switch to a heat pump
Comparison
Heat Pump vs Gas Boiler
20-year total cost of ownership
Grant Guide
Boiler Upgrade Scheme
£7,500 towards a heat pump
Blog
Off-Grid Heating Options Cornwall
All heating options for homes without mains gas
Service
Boiler Installation Service
Worcester Bosch, Vaillant, Ideal
Service
Heat Pump Installation
The long-term alternative to a new boiler