As a rough guide, most South West homeowners pay somewhere between £2,500 and £5,500 for an oil boiler replacement fully installed. A straightforward swap of an internal boiler sits towards the lower end. An external model, a tank replacement or a boiler that needs moving pushes the price up.
Oil heating is a fact of life across rural Cornwall and Devon. Large parts of both counties have no mains gas at all, so when the boiler that heats your home and hot water starts failing, an oil boiler replacement is not optional and the options can feel confusing. Kerosene boilers, combination oil boilers, internal versus external, tank rules, OFTEC paperwork. It is a lot to take in.
This guide sets out what actually affects the cost, what to check before you accept any quote, and why fixed pricing matters more with oil than with almost anything else in your home.
Why oil boiler replacement costs more than gas
Oil boilers are generally more expensive than their gas equivalents, both to buy and to fit. The market is smaller, the boilers are built with heavier heat exchangers, and the installation involves parts a gas job never touches: the fuel line from the tank, the fire valve, the filter and the burner setup. Commissioning an oil boiler also takes real skill. The burner has to be set up with a flue gas analyser and the fuel pressure checked, not just switched on and left.
That is why oil work should only ever be done by an OFTEC registered technician. OFTEC registration is the oil equivalent of Gas Safe registration, and it matters for your insurance, your warranty and your safety. DCI Boilers is OFTEC registered, so every oil installation we do is commissioned and certificated properly.
What drives the price up or down
Internal or external boiler
Internal oil boilers live in a kitchen, utility room or outbuilding. External models sit outside against a wall in a weatherproof casing, which frees up space indoors and keeps burner noise out of the house. External boilers typically cost a little more to buy, and swapping from internal to external (or the reverse) adds pipework and electrical work. A like-for-like swap in the same position is always the cheapest route.
Heat-only or combination
Most oil systems in older South West properties are heat-only, with a hot water cylinder. Oil combi boilers exist and can work well, but they are more expensive and suit some homes better than others. If your cylinder and controls are in good order, keeping the heat-only setup usually makes financial sense.
The condition of your oil tank
This is the one that catches people out. An oil tank has a working life, and a tank that is bulging, cracking, rusting or sitting on a failing base may need replacing at the same time as the boiler. Current standards also govern where a tank can sit, how far it must be from buildings and boundaries, and when a bunded (double-skinned) tank is required. A new tank and base is a significant extra cost, so any honest survey will look at the tank before quoting, not spring it on you halfway through the job.
Access and location
Plenty of oil-heated homes in Cornwall and Devon are exactly the sort of properties you would expect: farmhouses, cottages, homes down long lanes. Awkward access, long fuel line runs and solid stone walls can all add labour time. None of it is a problem for an experienced local installer, but it is another reason a fixed quote from someone who has actually seen the property beats any online estimate.
Typical ranges as a rough guide
- Like-for-like internal oil boiler swap: roughly £2,500 to £4,000 installed
- External oil boiler replacement: roughly £3,000 to £4,500 installed
- Replacement plus a new bunded tank: often £4,500 to £7,000 depending on tank size and base work
These are broad estimates, not promises. The boiler brand, output and warranty length all move the number, and so does everything above. The only accurate figure is a fixed quote for your actual home. DCI Boilers installs oil boilers with up to 12 year manufacturer warranties, and the price we quote up front is the price you pay.
Is it worth repairing instead?
Sometimes, yes. Oil boilers are mechanically simple in many ways, and a worn nozzle, a blocked filter or a failing photocell is a repair, not a replacement. If your boiler is under ten or twelve years old and the heat exchanger is sound, boiler repairs may be the right call. Replacement makes sense when the heat exchanger is corroding, parts are scarce, or breakdowns are becoming a yearly event. Regular boiler servicing is the best way to push that decision years into the future, because most oil boiler failures start as maintenance jobs that were skipped.
And if you are on mains gas rather than oil, the numbers are different again. See our guide to gas boiler replacement instead.
How DCI Boilers can help
DCI Boilers carries out oil boiler replacement across Cornwall and Devon from our base near Saltash, with OFTEC registered engineers, fixed upfront pricing and boilers backed by up to 12 year manufacturer warranties. We survey the whole system, tank included, before we quote, so there are no surprises once work starts. If your oil boiler has died completely and you are without heat, we also run a 24/7 emergency boiler call-out service.
Need help now? Call DCI Boilers on 07888 862 603 or get a free quote.
Frequently asked questions
How long does an oil boiler replacement take?
A like-for-like swap is usually one to two days. Add a tank replacement or a change of boiler position and it can stretch to three or four. Your quote should set out the timescale before anyone lifts a tool.
Do I have to replace my oil tank at the same time?
Only if it needs it. A sound, correctly sited tank can stay. But if the tank is deteriorating or does not meet current siting and bunding standards, replacing it alongside the boiler is cheaper and less disruptive than doing it separately a year later.
Should I switch from oil to a heat pump instead?
For some homes it is worth exploring, and grant schemes exist for certain households, though eligibility varies and is never guaranteed. For many older, stone-built South West properties a modern oil boiler remains the practical, affordable choice today. We will give you an honest view either way.
Why does OFTEC registration matter?
OFTEC is the competent person scheme for oil heating. An OFTEC registered technician can self-certify the installation, commission the burner correctly and issue the paperwork your warranty and insurance rely on. Unregistered installation risks all three.