Boilers and Heating Systems in London: Replacement, Heat Pumps and What to Expect in 2026

Current position (2026): gas boilers remain legal to install in existing homes. The government consulted on a 2035 deadline for phasing out the installation of new gas and oil boilers in existing homes, but as of 2026 the specific form of any legislation remains under development. The Future Homes Standard (primarily applicable to new-build homes) has been clarifying, but existing home rules remain less certain.

What this means practically: if your boiler fails or needs replacing in 2026, you can still install a new gas boiler. A modern condensing combi boiler has a lifespan of 10 to 15 years. Whether the boiler you install today will need replacing before gas is phased out depends on policy decisions not yet finalised.

Combi versus system boiler: a combi (combination) boiler provides both central heating and domestic hot water on demand without a hot water storage cylinder. It is the most common boiler type in London flats and terrace houses. A system boiler works with a separate hot water cylinder — more suitable for larger households with higher hot water demand.

Signs that replacement is more cost-effective than continued repair:

• The boiler is more than 12 to 15 years old
• Repair costs are high relative to the cost of a replacement
• The boiler is not a condensing (high-efficiency) type (older non-condensing boilers are significantly less efficient)
• Energy bills are rising despite unchanged usage

A modern A-rated condensing boiler (ErP rating A) operating at 90 to 95 per cent efficiency will use meaningfully less gas than an older boiler operating at 70 to 80 per cent efficiency.

Typical cost of a replacement gas combi boiler in London (2026): £1,800 to £3,500 installed (supply and installation of a mid-range combi, including removing the old boiler and updating controls).

Air source heat pumps (ASHPs) extract heat from outdoor air and use it to heat the home and hot water. They are more efficient than gas boilers in energy conversion terms (typically achieving 2.5 to 4 units of heat for every unit of electricity consumed — a coefficient of performance of 2.5 to 4). However, electricity costs significantly more per unit than gas in the UK, which reduces the running cost advantage.

Key factors determining heat pump suitability for a London home:

1. Insulation: heat pumps work at lower flow temperatures than gas boilers (typically 35 to 55 degrees C versus 65 to 75 degrees C). To deliver adequate heat to the rooms at lower flow temperatures, the home needs to be well-insulated. A poorly insulated Victorian terrace with significant heat loss may require very large radiators or underfloor heating throughout to work efficiently with a heat pump. Improving insulation before or alongside a heat pump installation significantly improves performance.

2. Radiator sizing: existing radiators sized for high-temperature gas heating will typically need to be replaced with larger-surface radiators designed for low-temperature operation, or supplemented by additional radiators. This is a significant additional cost often not communicated upfront.

3. Outdoor space: a typical ASHP requires an outdoor unit roughly the size of a large suitcase or air conditioning outdoor unit. In London terrace houses with limited outdoor space, finding a suitable location that also complies with permitted development rules and does not cause noise nuisance to neighbours requires careful assessment.

4. Running costs: in 2026, electricity costs approximately 24p per kWh versus gas at approximately 6 to 7p per kWh. Even at a COP of 3, a heat pump running on electricity costs more per unit of heat than a gas boiler. The economics improve if the home has solar panels (reducing the effective cost of electricity) or if time-of-use electricity tariffs are used.

5. Grants: the Boiler Upgrade Scheme (BUS) provides a £7,500 grant toward the installation of an ASHP in an eligible home. This grant significantly improves the economics of early adoption.

6. Planning considerations: heat pumps installed on external walls or in gardens of houses are generally permitted development, subject to noise and proximity conditions. Listed buildings and some conservation areas may require consent.

Underfloor heating (UFH) is particularly well-suited to low-temperature heat pump operation. Water-based UFH operates at 35 to 45 degrees C — perfectly matched to heat pump output. Retrofitting wet UFH beneath existing floor finishes is possible (particularly with retrofit-profile low-profile systems), though it involves significant disruption and cost compared to new-build or extension installation.

Electric UFH (underfloor heating mats or cables) is less expensive to install but significantly more expensive to run than water-based systems on mains electricity tariffs.

• Boiler needs immediate replacement and budget is constrained: install a modern condensing gas combi boiler. This is the lowest short-term cost and defers the heat pump decision.
• Planning a major refurbishment or extension: this is the optimal moment to assess heat pump viability — insulation can be improved, underfloor heating can be installed, and radiators can be upsized as part of the wider project.
• Long-term energy cost reduction and environmental priority: assess the full-fabric approach first (insulation, draught-proofing, windows) to reduce heat demand before sizing a heat pump.