The fastest way to cut your heating costs in London is to lower your boiler’s flow temperature, heat only when you need it, and fix the small efficiency leaks in your system. A boiler that is 15 years old or more, or rated E, F or G, is often the biggest cost. Replacing it with a new energy efficient boiler can save roughly £80 to £250 a year on gas, depending on how inefficient the old one is and how much heat your home uses.
Gas is the main cost. The Ofgem price cap for 1 October to 31 December 2026 is £1,723 a year for a typical Direct Debit household, up 4% on the last period. The rise comes from higher wholesale gas prices. That makes every wasted kilowatt hour more expensive than it was last winter.
This guide covers what your boiler costs to run, which settings save money, whether to leave the heating on all day, and when a new boiler pays for itself.
Quick Answers
| Question | Short answer |
|---|---|
| Best boiler flow temperature? | About 55–60°C for radiators, if your home stays warm |
| Best room temperature? | 18–21°C, with living rooms at the top of that range |
| Is it cheaper to leave heating on all day? | Usually no. Use a timer instead |
| Does turning the heating down save money? | Yes. Each 1°C lower can save around 10% |
| Does a new boiler cut bills? | Yes. Savings are biggest when replacing a boiler rated G, F or E |
| Most efficient boiler type? | A condensing gas boiler with an ErP efficiency of 92% or higher |
How Much Does It Cost to Run a Boiler in London?
A typical London home spends about £700 to £900 a year on gas. That covers heating and hot water. Larger or older properties cost more.
Ofgem now bases its typical household bill on 9,500 kWh of gas and 2,500 kWh of electricity a year. On that use, the average gas bill under the current cap comes to about £865 a year, including the standing charge. The average gas unit rate on a Direct Debit tariff is 7.97p per kWh, so I’ve used a round 8p in the examples below. Your rate may differ slightly by region and tariff.
Central Heating Cost Per Hour
A boiler running in a typical London home costs roughly 60p to £1.50 for each hour it is actively heating. This is an estimate, because boilers do not run flat out all the time.
A 24kW boiler at full power burns about 26 kWh of gas an hour. At 8p per kWh, that is around £2 an hour. In practice, modern boilers modulate. They turn their output down once the house is warm, so the real average is lower. A small flat sits at the bottom of the range, and a large, draughty Victorian house sits at the top.
Illustrative Annual Gas Costs in London Homes
| Home type | Typical annual gas use | Unit cost at 8p/kWh |
|---|---|---|
| 1-bed flat | 5,000 kWh | about £400 |
| 2-bed flat or terrace | 9,500 kWh | about £760 |
| 3-bed semi | 12,000 kWh | about £960 |
| 4-bed Victorian house | 17,000 kWh | about £1,360 |
These are examples, not quotes. On top of the unit cost, the average gas standing charge is 29.68p per day, which is about £108 a year whatever you use. Standing charges are fixed, so all the savings in this guide come from using less gas.
Prices may keep rising. Forecasts point to a further 9% increase in the price cap in early 2027. Treat that as a forecast, not a promise.
Is an Old Boiler Expensive to Run?
Yes. An old non-condensing boiler often wastes 25–40% of the gas it burns, while a modern condensing boiler wastes 10% or less.
Boilers from before the mid-2000s were often only 60–70% efficient. For every £1 of gas, they sent only 60–70p of heat to your radiators. The rest left through the flue. Condensing boilers have been required in new gas installations in England since 2005. Many homes still have older models, and some condensing ones from the 2000s have lost efficiency through poor maintenance.
How to tell if your boiler is energy efficient:
- Check the age. A boiler over 15 years old is very likely to be less efficient.
- Look at the label or manual. Look for an efficiency percentage or an A–G band. Bands E, F and G are poor.
- Look at the flue. A visible white plume outside is normal for a condensing boiler in cold weather. A boiler that never produces one may not be condensing.
- Check your bills. A big jump in gas use with no change in habits can point to a failing system.
- Ask a Gas Safe registered engineer. They can measure efficiency and check your controls.
What Temperature Should I Set My Boiler To?
Set your boiler flow temperature to about 55–60°C. Then raise it only if your home does not get warm enough.
Boiler Flow Temperature
The flow temperature is the temperature of the water your boiler sends to the radiators. Many boilers are set to 70–80°C from the factory. That is often hotter than needed.
Condensing boilers work best when the water returning to them is below about 55°C. At that point, the boiler captures extra heat from its exhaust gases. A very high flow temperature stops this from happening, and you burn more gas for the same warmth.
How to lower it:
- Find the heating temperature dial on your boiler.
- Reduce it to around 60°C, then try 55°C.
- Give the house a day or two to settle.
- If rooms are not warm enough, go up by 5°C.
Radiators will feel less hot to the touch, which is normal. The house should warm up more slowly but reach the same temperature. Only adjust the dial your manual describes. If you are unsure, ask your engineer at the next service.
Hot Water Temperature
On a combi boiler, hot water is heated on demand, so a setting of around 50–55°C is usually enough. If you have a hot water cylinder, it should store water at 60°C or above to control legionella bacteria. Do not lower a cylinder below that to save money.
What Temperature Should My Central Heating Be?
Your central heating should be set between 18°C and 21°C. The World Health Organization and UK public health bodies treat 18°C as a healthy minimum for most adults. Babies, older people and anyone with a health condition may need it warmer.
| Room | Suggested temperature |
|---|---|
| Living room | 20–21°C |
| Kitchen | 18–19°C |
| Bedrooms | 16–18°C |
| Bathroom | 20–22°C while in use |
| Hallways and spare rooms | 16–18°C |
Does Turning the Heating Down Save Money?
Yes. Lowering your thermostat by 1°C can cut your heating bill by around 10%. That figure is widely quoted, but the exact saving depends on your home. A well-insulated flat saves less in pounds than a leaky house because it uses less heat to begin with.
A good habit is to drop the thermostat by 1°C for a week and see if you notice. Most people don’t.
Does Turning the Boiler Off Save Money?
Yes. Turning your heating off when nobody is home, or when you are asleep and warm under a duvet, saves gas. A house loses heat faster the warmer it is compared with outside, so keeping it hot when empty just wastes energy.
Should you turn your boiler off when you leave the house? Yes, if you will be out for several hours. The simplest way is a timer or programmer that switches the heating off for you.
Good Times to Switch It Off
- During working hours if the house is empty
- At night, once you are in bed
- In spring and autumn on mild days
- During summer, using the hot water setting only
Two Warnings
- Do not turn the boiler fully off in freezing weather. London still gets frosty nights. Use your boiler’s frost protection or set the thermostat to around 5–10°C to protect pipes when you are away.
- Do not let a home get cold and damp. A cold house with poor ventilation can develop condensation and mould. That costs more to fix than the gas you saved.
In summer, run the heating for a few minutes once a month. This keeps the pump and valves from seizing.
Is It Cheaper to Leave Heating On All Day?
For most London homes, no. Heating on a timer is usually cheaper than leaving it on all day.
The reason is simple. A heated home is always losing heat through walls, windows, roofs and floors. The longer it stays warm, the more heat it loses in total. Heating only when needed cuts those losses.
The “Constant Low” Myth
Many people believe that keeping the heating on low all day is cheaper than warming the house up from cold. For a gas boiler, that is generally not true. The boiler still has to replace the heat the house loses, and it loses more over 24 hours than it would over 8 or 10.
When Constant Heating Can Make Sense
- Heat pumps. They work best running steadily at low temperatures.
- Very well-insulated homes. Some new-builds and retrofitted properties hold heat for hours.
- Health needs. If someone at home is frail, very young or unwell, warmth matters more than the saving.
- Damp or mould problems. A steady background temperature can help.
A Better Plan Than All-Day Heating
Set the heating to come on 30 to 60 minutes before you wake up and before you get home. Switch it off shortly before you leave or go to bed, because the house will stay warm for a while. A smart thermostat can learn how fast your home heats up and time this automatically.
How Can I Make My Boiler More Efficient?
The most effective steps are servicing your boiler, lowering the flow temperature, balancing your radiators and improving your controls. Most cost little or nothing.
Step-by-Step: Improve Boiler and Heating Efficiency
- Book an annual boiler service. A Gas Safe registered engineer will clean, test and adjust the boiler. Servicing also keeps most warranties valid.
- Lower the flow temperature. Try 55–60°C as described above.
- Bleed your radiators. Trapped air leaves cold patches at the top. Bleed each radiator with a radiator key and top up the boiler pressure if needed (typically 1–1.5 bar when cold, but check your manual).
- Balance the system. If some radiators are hot and others barely warm, the flow needs balancing. An engineer can do this in a visit.
- Fit thermostatic radiator valves (TRVs). They stop rooms overheating and let you set each room separately.
- Add a room thermostat or smart thermostat. Choose one that lets you set schedules and reacts to the weather.
- Fit a magnetic filter. It catches sludge in the system. Sludge makes the boiler work harder and shortens its life.
- Consider a powerflush if radiators heat unevenly. This removes heavy sludge from older systems.
- Insulate pipes and hot water cylinders. This keeps heat where it is needed.
- Improve your home’s insulation. A boiler cannot fix a house that leaks heat.
What Is the Most Efficient Way to Heat a London Home?
For most existing homes, the most efficient approach is a properly sized, well-controlled condensing boiler, combined with good insulation and lower flow temperatures. Heat pumps are more efficient in principle, but they need suitable insulation, space and upfront investment. The government’s Boiler Upgrade Scheme has offered grants towards heat pumps in England, so check the latest terms before deciding.
How Can I Reduce My Heating Bill in London?
Reduce your heating bill by using less heat, keeping the heat you make, and choosing the right tariff. Here are the most useful actions, roughly in order of cost.
Free or very low cost
- Lower your thermostat by 1°C
- Use timers and zones
- Close doors to unused rooms
- Close curtains at dusk
- Bleed radiators
- Move furniture away from radiators
Low cost
- Draught-proof doors, letterboxes and gaps at skirting boards
- Fit reflective foil behind radiators on external walls
- Add TRVs and a smart thermostat
- Use secondary glazing or thick curtains on single-glazed sash windows
Medium cost
- Top up loft insulation to around 270mm
- Insulate floors and cavity or solid walls where possible
- Fit a magnetic filter or powerflush
Higher cost
- Replace an old boiler with an energy efficient boiler
- Install double glazing or heritage-friendly windows
- Add solid wall insulation or a heat pump where suitable
London-specific factors
- Many Victorian and Edwardian homes have solid brick walls with no cavity. They lose more heat than modern homes, so draught-proofing and loft insulation matter a lot.
- In converted flats, you may need your freeholder’s permission for a new flue or pipework. Check your lease before booking work.
- Some blocks have communal heating. In that case, your control options and tariff differ, so ask your managing agent.
Check your tariff. Around 11 million households were on fixed tariffs as of August 2026, and they were not affected by the latest cap change. If a fixed deal is available at a price you are comfortable with, compare it with the cap. Do not assume it is cheaper, since fixed prices can be higher than the cap.
Are Modern Boilers More Efficient?
Yes. Modern condensing boilers are typically 88–94% efficient, compared with 60–75% for many older boilers.
Condensing technology recovers heat that older boilers let escape. New gas boilers in England must also meet the Boiler Plus standard. That means a minimum ErP efficiency of 92%, with time and temperature controls. Combi boilers need at least one extra energy-saving feature, such as weather compensation, load compensation, flue gas heat recovery or a smart thermostat with automation.
Old vs Modern Boiler Comparison
| Feature | Old non-condensing boiler | Modern condensing boiler |
|---|---|---|
| Typical efficiency | 60–75% | 88–94% |
| Efficiency rating band | Often E, F or G | Usually A |
| Modulation | Limited | Adjusts output to demand |
| Controls | Basic timer | Smart, weather-aware options |
| Heat wasted | 25–40% | 6–12% |
| Warranty | Usually expired | Often 7–12 years with servicing |
Real-world efficiency is often slightly lower than the label figure, especially if the flow temperature is too high or the system is unbalanced. That is why controls and settings matter as much as the boiler itself.
Does a New Boiler Reduce Energy Bills?
Yes. A new boiler will lower your gas use if it replaces an inefficient one, especially when installed with good controls. The saving depends on how efficient your current boiler really is.
How Much Money Can a New Boiler Save Each Year?
This worked example uses a typical 9,500 kWh of gas a year, a 90% real-world efficiency for the new boiler, and a gas price of 8p per kWh. It is an illustration, not a guarantee.
| Your old boiler’s efficiency | Gas needed with old boiler | Gas needed with new boiler | Estimated yearly saving |
|---|---|---|---|
| 60% | 9,500 kWh | about 6,300 kWh | about £250 |
| 70% | 9,500 kWh | about 7,400 kWh | about £170 |
| 80% | 9,500 kWh | about 8,400 kWh | about £85 |
The larger your home and the higher your gas use, the bigger the saving. A 4-bed Victorian house using 17,000 kWh could save roughly 80% more than the figures above. Adding a smart thermostat, TRVs and a lower flow temperature can push savings higher.
Should I Replace My Old Boiler to Save Money?
Replace it if it is old, inefficient or unreliable. Do not replace a working boiler that is only a few years old and still efficient just to chase a small saving.
A new boiler is worth serious thought when:
- Your boiler is over 15 years old
- It has an efficiency band of E, F or G
- Repairs are getting frequent or expensive
- Spare parts are hard to find
- Your gas bills have risen with no change in habits
- Your engineer has advised against another repair
It may be worth waiting when:
- Your boiler is under 10 years old and rated A or B
- It is serviced yearly and runs well
Be realistic about payback. On energy savings alone, a new boiler in London can take 10 years or more to pay for itself. Faster payback comes from combining lower gas use with avoided repair bills and better comfort.
Does a New Combi Boiler Use Less Gas?
Usually yes. A modern combi has higher efficiency and no hot water cylinder losing heat all day. The saving is largest if you swap an old regular or system boiler and cylinder for a well-sized combi. However, a combi is not always right for a large family with several bathrooms. In that case, a system boiler with a cylinder may give better hot water flow.
What Is the Most Energy Efficient Boiler for a London Home?
The best energy efficient boiler for your London home is a condensing gas boiler with an ErP efficiency of 92% or higher. It should be sized to your home’s heat demand and paired with smart controls.
Bigger is not better. An oversized boiler switches on and off too often, wastes gas and wears out sooner. A qualified engineer should calculate your heat loss room by room before recommending an output.
What to look for in a high efficiency boiler:
- ErP efficiency of 92% or above, ideally 94% or more
- Good modulation, so it can run at low output most of the time
- Weather or load compensation, to match output to conditions
- A compatible smart thermostat
- A long warranty (often 7–12 years when the boiler is installed and serviced by an approved installer)
- A reliable brand with local parts and support. Established makers such as Worcester Bosch, Vaillant, Viessmann and Ideal all offer high efficiency ranges. The best choice depends on your home and quote.
Combi, system or regular?
| Type | Best for | Watch out for |
|---|---|---|
| Combi | Flats and small to medium homes with 1–2 bathrooms | Lower hot water flow if several taps run at once |
| System | Larger homes with several bathrooms | Needs space for a cylinder |
| Regular (heat only) | Homes with existing tanks and older systems | Larger, and more complex to install |
Boiler Replacement and Installation in London: Cost and What to Expect
A new boiler installation in London typically costs about £2,500 to £4,000 for a like-for-like combi swap. Conversions and system boiler installs often cost £3,500 to £6,000 or more. London labour and parking costs push prices above the national average. Treat these as ballpark ranges and get at least two written quotes.
What Affects Boiler Replacement Cost in London
- Boiler type and brand
- Whether you are swapping like for like or converting
- Moving the boiler to a new position
- Flue and condensate pipe routing (often trickier in flats)
- Extras such as a magnetic filter, powerflush, smart thermostat and TRVs
- Access, parking and building rules
What Should Be Included in a Quote
- A heat loss calculation or clear sizing advice
- Removal and disposal of the old boiler
- A new flue, condensate pipework and filter
- System cleaning and inhibitor
- Boiler Plus-compliant controls
- Commissioning, plus registration of the installation with Gas Safe or the appropriate scheme
- Warranty details and the terms for keeping it valid
Choosing an Installer
Always use a Gas Safe registered engineer, and ask to see their ID card. Check that their listing covers the type of work. Ask for reviews, insurance details and a written quote. If you rent or own a leasehold flat, check permission requirements before you book.
Frequently Asked Questions
1. How much does it cost to run a boiler per hour?
A typical London home spends about 60p to £1.50 for each hour the boiler is heating. A 24kW boiler at full power can cost around £2 an hour, but most boilers run below full power most of the time.
2. What temperature should I set my boiler to save money?
Set the heating flow temperature to around 55–60°C. Combi hot water can stay around 50–55°C, while a hot water cylinder should stay at 60°C or above for safety.
3. Is it cheaper to leave central heating on low all day?
Usually not. A house loses more heat over 24 hours than over a shorter heating period, so timed heating normally costs less. The exceptions are heat pumps, very well-insulated homes and health needs.
4. Should I turn my boiler off when I leave the house?
Yes, if you will be out for several hours. Use a timer or smart thermostat, and keep frost protection on in winter.
5. Does turning the heating down save money?
Yes. Lowering the thermostat by 1°C can save around 10% on heating costs, though the exact figure varies by home.
6. Will a new boiler reduce my energy bills?
Yes, especially if your old boiler is rated E, F or G or is over 15 years old. Bills fall further if the new boiler is paired with better controls.
7. How much money can a new boiler save each year?
A typical London home might save around £85 to £250 a year on gas, depending on the old boiler’s efficiency. Larger homes with higher gas use save more.
8. Is an old boiler expensive to run?
Yes. Older boilers can waste 25–40% of their gas, and they often need more repairs.
9. How do I know if my boiler is energy efficient?
Check its age, efficiency band and manual. A condensing boiler with an ErP efficiency of 92% or above is efficient. An engineer can test it for you.
10. How can I make my central heating more efficient?
Service the boiler, lower the flow temperature, bleed and balance radiators, fit TRVs, use a smart thermostat, and improve insulation and draught-proofing.
Conclusion
Reducing heating costs in London comes down to three moves: use less heat, waste less of it, and burn gas in an efficient boiler. Start with the free steps. Lower your flow temperature, trim your thermostat by a degree, and set a sensible timer. Then look at your boiler’s age and efficiency. If it is over 15 years old, rated E, F or G, or costing you more in repairs each winter, a new energy efficient boiler is likely to pay you back in lower bills and fewer breakdowns.
If you are weighing up a boiler replacement in London, the next step is simple. Book a survey with a Gas Safe registered engineer, ask for a heat loss calculation, and compare written quotes for boiler installation. A good installer will tell you honestly whether you need a new boiler or just a service and better controls.
