Oil Combi Boiler 2026: Grants, Costs & Best Options

What Is an Oil Combi Boiler and Is It Right for Your Home?

An oil combi boiler heats your water on demand from a tank of oil stored outside, with no hot water cylinder needed indoors. It works exactly like a gas combi, just with a different fuel feeding it.

That distinction matters because roughly 1.5 million UK homes are off the gas grid. Most of them sit in rural areas of Scotland, Wales, Northern Ireland, and the West Country. If your neighbours are burning oil too, you'll know.

The combi version is the modern default. Older oil heating systems use a regular boiler paired with a hot water cylinder in an airing cupboard, which is fine if you've got a big family and four bathrooms running simultaneously, but most households don't need that much stored hot water sitting around losing heat.

So when does a combi make sense? One bathroom, maybe two. A household of one to four people. Decent mains water pressure. If you've got five bedrooms and three showers running at 7am, stick with a regular boiler and cylinder, the combi won't keep up.

We see a lot of people in Cornwall and rural Devon swap a 20-year-old regular oil boiler for a combi when they extend or refit a kitchen. It frees up the airing cupboard. That's often the real reason people make the switch, not efficiency.

One honest thing to say up front. The government doesn't want you installing a new oil boiler in 2026. Off-gas homes are the priority for the heat pump rollout, and the policy direction is clear. Whether that's right for your situation is a separate question, and we'll come back to it.

How Much Does an Oil Combi Boiler Cost to Install in 2026?

Expect £2,500 to £4,500 for a straight swap, including the boiler, labour, flue, and basic pipework. New installs with relocated tanks and fresh oil lines run higher.

Here's the breakdown most installers will quote against:

The boiler itself is usually £1,200 to £2,000 for a Worcester Bosch Greenstar Heatslave, Grant Vortex, or Warmflow Agentis. Labour and ancillaries make up the rest.

Oil prices change everything about running costs. At the time of writing, kerosene sits around 60 to 75 pence per litre, and a four-bedroom home will burn roughly 1,500 to 2,000 litres a year. That's £900 to £1,500 annually on fuel alone, before you factor in servicing.

Servicing matters more with oil than gas. A neglected oil boiler will gum up the burner, drop efficiency hard, and eventually fail in the middle of January. Budget £120 to £180 a year for an annual service. Skip it and you'll regret it.

Can You Get a Grant for an Oil Combi Boiler in 2026?

Not directly, no. There is no government grant scheme in 2026 that pays toward installing a new oil combi boiler as a like-for-like replacement.

The Boiler Upgrade Scheme specifically excludes fossil fuel boilers. Its purpose is to shift homes onto low-carbon heating, so the £7,500 grant only applies to air source heat pumps, ground source heat pumps, biomass boilers, and a couple of newer categories. Oil is the fuel the scheme is designed to replace, not subsidise.

ECO4 is the only route where an oil boiler replacement is sometimes funded, and even then it's complicated. We'll cover it properly in the next section.

The Great British Insulation Scheme closed in March 2026, so that's no longer a live option. Some installers still mention it in their literature, which is misleading. Ignore it.

What about local authority schemes? A handful of councils run discretionary grants for off-grid homes, particularly in Cornwall, Devon, Northumberland, and parts of rural Wales. These come and go. Worth a phone call to your council's energy team, but don't bank on it.

Here's what most guides won't tell you. The honest answer is that if you want a new oil boiler, you're paying for it yourself. The grant system has moved on. That's not necessarily a bad thing, oil heating is expensive to run and the policy environment is only going to get tighter, but it does mean the financial maths is shifting away from oil whether you like it or not.

ECO4 and the Boiler Upgrade Scheme: Which Could You Qualify For?

ECO4 might fund a replacement oil boiler if you receive qualifying benefits and a heat pump isn't suitable for your home. The Boiler Upgrade Scheme pays £7,500 toward a heat pump but excludes oil boilers entirely.

The two schemes work in completely different ways, so it helps to look at them separately.

ECO4 is funded by the big energy suppliers and managed through Ofgem. It targets households on means-tested benefits including Universal Credit, Pension Credit, Child Tax Credit, and a handful of others. If you qualify on income, the scheme pays for energy efficiency upgrades in full. The catch is that ECO4 is heat-pump-first for off-gas homes. Your installer has to demonstrate that a heat pump isn't viable before they'll fund an oil replacement, and the threshold for that is high. Small kitchen, no space for a hot water cylinder, listed building, that kind of thing. We've covered the full ECO4 eligibility rules separately.

The Boiler Upgrade Scheme is universal. No means test, no benefits requirement. Anyone with a property in England or Wales can apply. The grant is £7,500 toward an air source or ground source heat pump, £5,000 toward a biomass boiler, or £2,500 toward an air-to-air system or heat battery. The scheme runs until March 2030, which gives you genuine time to plan rather than rush. Full detail in our Boiler Upgrade Scheme guide.

So what should you actually do?

If you're on benefits and your home is suitable for a heat pump, ECO4 funds the whole heat pump install. That's the best outcome.

If you're not on benefits but you've got a reasonable property, BUS knocks £7,500 off a heat pump install, leaving you paying £3,000 to £6,000 typically. Still meaningful money, but the running costs drop hard once you're off oil.

If neither route works for you, you're paying full price for whatever you install. At that point, the choice between oil combi and heat pump comes down to your specific home and how long you plan to stay there.

Oil Combi vs Heat Pump: Which Makes More Sense Off the Gas Grid?

For most well-insulated rural homes, a heat pump is the better long-term choice in 2026. For poorly insulated period properties with cold radiators, an oil combi still has a real case.

Here's the honest comparison, with no greenwashing and no fossil-fuel romance:

The running cost comparison shifts year by year with oil prices and electricity tariffs. If you've got an Octopus Cosy or Agile tariff feeding a heat pump, the numbers look great. If you're on a standard variable tariff, they look less great.

The radiator question is the one most installers won't be straight with you about. Heat pumps run at lower flow temperatures than oil boilers, around 45 to 55 degrees rather than 70 to 80. If your radiators are sized for high-temperature heat, you'll either feel cold or need bigger radiators. That's another £1,500 to £3,500 of work that doesn't show up in the headline BUS-adjusted figure.

Our view? If your home is properly insulated to a decent EPC C or better, and you've got space outside for the unit, the heat pump wins on a 15-year horizon. The £7,500 BUS grant tips the maths firmly in that direction. If you're in a poorly insulated 1850s farmhouse with single skin walls and you can't justify retrofitting, an oil combi keeps you warm and the maths is what it is. There's no shame in that.

Anyway. The decision often comes down to how much disruption you can tolerate and how long you're staying. Replacing a boiler is a one-day job. Installing a heat pump properly is a one to two-week project with a lot of dust.

How to Choose a Reliable Oil Combi Boiler for a UK Home

Stick with Grant, Warmflow, Worcester Bosch, or Firebird. Avoid anything you can't get a UK service engineer for within 48 hours.

The oil boiler market is smaller than the gas market, so brand choice is genuinely narrower. Four manufacturers dominate UK installs and between them they cover roughly 85% of what gets fitted. Pick one of them and you'll have access to parts and engineers for the next 15 years, which matters more than a £200 saving on the upfront price.

Grant Vortex is the workhorse most rural installers default to. Reliable, easy to service, parts available everywhere. The Pro model is genuinely good. Worcester Bosch Greenstar Heatslave II has a bit more sophistication on controls and integrates well with smart thermostats. Warmflow Agentis is popular in Northern Ireland and the borders, built tough. Firebird Envirogreen is the value pick.

Things that actually matter when you choose:

The kW rating must match your home. A four-bed needs roughly 21 to 26 kW. Oversizing is the most common installer error, and an oversized combi cycles on and off constantly, wears out faster, and runs at lower efficiency.

Hot water flow rate matters more than central heating output for most households. Look at the litres per minute spec at a 35 degree temperature rise. Anything under 12 litres per minute will feel weak in a shower.

Warranty length tells you what the manufacturer thinks of their own product. Seven to ten years is now standard. Two-year warranties are a warning.

The installer matters as much as the boiler. OFTEC registration is the oil equivalent of Gas Safe, and your installer must hold it. Check the register directly, don't take their word for it. Ask for two local references from jobs done more than three years ago, recent installs always look fine, what you want to know is how the work held up.

One last thing. If you're getting quotes, get three. Always. The spread on oil boiler installs in the same village can be £1,800, and the most expensive isn't usually the best. Our guide to getting a new boiler quote covers the questions to ask and the red flags to watch for.

And if you're not sure whether oil is still the right answer at all, the eligibility checker will tell you in two minutes which grants apply to your specific situation, including the heat pump routes that might genuinely change the calculation.