How much can I save by replacing an old boiler with an A-rated one?

The Energy Saving Trust puts the annual saving from replacing a G-rated gas boiler with an A-rated one, with full controls, at £170 for a mid-floor flat to £500 for a detached house (£350 for a semi), at July 2026 fuel prices. The figures assume a new A-rated condensing boiler with a programmer, room thermostat and thermostatic radiator valves, replacing an older boiler with a programmer and room thermostat. Savings from a D-rated boiler are smaller: £90 (flat) to £220 (detached). The Energy Saving Trust puts the average cost of the replacement at £3,500 in Great Britain.

What is ErP and how does it relate to A-G ratings?

ErP (Energy related Products) is the EU / UK framework for rating boiler efficiency, mandatory on all new UK boilers since 2015. ErP rates seasonal space heating efficiency (ETAs) and hot water heating efficiency (etaWH) on an A-G scale, where A is the most efficient. All modern condensing boilers achieve ErP A-rated for space heating; hot water ratings vary (an A-rated combi might be B-rated for hot water depending on the model). The headline A-G rating is the space heating figure.

Will replacing my boiler improve my EPC?

Yes, but the uplift is modest in isolation. A boiler upgrade typically lifts an EPC by 4-12 points (one third to one full band). The bigger EPC levers are insulation (loft + cavity wall + solid wall), double / triple glazing, and renewable heat (heat pump or solar thermal). Combined with insulation, a boiler upgrade can move a property from EPC D to C or from C to B, which is meaningful for rental properties (the Minimum Energy Efficiency Standard threshold for new rentals is EPC E, and proposals to raise this to C were paused but may return).

UK 2026 / June 2026

Boiler efficiency ratings UK

Replacing a G-rated boiler with a modern A-rated condensing boiler and full controls saves £170 to £500 a year depending on the home: £170 in a mid-floor flat, £350 in a semi, £500 in a detached house (Energy Saving Trust, fuel prices as of July 2026).

The ErP A-G band ladder

All UK boilers sold since 2015 carry an ErP (Energy related Products) efficiency label on the same A-G scale used for white goods. A is most efficient (90%+ seasonal efficiency); G is least efficient (under 70%). Below is the band ladder with the typical home heating context for each:

A90%+Modern A-rated condensing combi. ErP target for all new replacements.

B86-90%Older condensing boiler (~2005-2010). Still efficient; consider replacement at 12+ years.

C82-86%Pre-condensing era.

D78-82%1990s typical. Eligible for ECO4 if household qualifies on benefits.

E74-78%1980s typical. Significant gas waste; high-priority for replacement.

F70-74%Pre-1980s. ECO4 prioritises F and G rated homes.

GBelow 70%Old non-condensing boilers, including many back boilers. The biggest saving from replacement: £170-£500 a year (Energy Saving Trust).

What "condensing" means

A condensing boiler recovers heat from the flue gases that older (non-condensing) boilers vent straight outside. The recovered heat preheats return water, lifting overall efficiency from ~78-82% (non-condensing) to ~90-94% (condensing). Condensing has been mandatory on all UK gas boiler installations since April 2005 under Building Regulations Part L, so any boiler installed before then is non-condensing and typically pre-A-rated. Replacement is almost always the right call for boilers older than 20 years.

Annual gas saving by current band

Energy Saving Trust estimates for England, Scotland and Wales, based on fuel prices as of July 2026, for a new A-rated condensing boiler with programmer, room thermostat and TRVs replacing an older boiler with programmer and room thermostat:

Old boiler	Mid-floor flat	Mid-terrace	Semi-detached	Detached bungalow	Detached house
G (under 70%)	£170	£270	£350	£320	£500
F (70-74%)	£120	£180	£240	£220	£350
E (74-78%)	£100	£160	£210	£190	£270
D (78-82%)	£90	£140	£190	£170	£220

Annual savings per year. Source: Energy Saving Trust, Boiler types explained. Savings vary with the size and thermal performance of your home.

How to lift efficiency beyond A-rated

Smart thermostat with weather compensation: drops flow temperature when outdoor temperature is mild. Boiler Plus 2018 makes this (or equivalent) mandatory on new combi installs in England.
Flue gas heat recovery (FGHR): passive bolt-on device that pre-warms incoming cold water using waste flue heat. Recovers an extra 2-4 percentage points of efficiency. £250-£400 fitted.
TRVs on every radiator: thermostatic radiator valves let each room set its own temperature. Standard on most new installs but still missing on many older properties.
Insulation: cavity wall (£400-£600) and loft top-up (£200-£400) typically save more per year than the boiler upgrade itself.
Hot water cylinder jacket: £20-£40 for a factory-foam-equivalent jacket on an uninsulated cylinder. Pays back in 6-12 months.

FAQ

How much can I save replacing a G-rated boiler with A-rated?

£170 (mid-floor flat) to £500 (detached house) a year; £350 for a semi-detached house. Energy Saving Trust, fuel prices as of July 2026.

What is ErP?

Energy related Products - the UK / EU efficiency labelling framework, mandatory on all new UK boilers since 2015. Uses the same A-G scale as white goods.

Does a new boiler improve my EPC?

Yes, by 4-12 points typically (one third to one full band). Bigger gains from combined insulation + boiler upgrade.

What's the most efficient combi boiler in 2026?

Every new gas boiler sold in the UK is a condensing boiler, and the difference in rated seasonal efficiency between models is a few percentage points. Compare each model's ErP product fiche, and set up the controls (flow temperature, weather or load compensation): that usually matters more than the badge.

Is a heat pump more efficient than an A-rated combi?

Yes by a wide margin on raw efficiency (300% vs 93% typical). But running cost is closer to break-even because UK electricity costs ~4x gas per kWh. Combined with the higher upfront cost, the case for switching is strongest in already-well-insulated homes.

Old boiler eating bills? Start with 8 signs you need a new boiler and repair or replace. Considering heat pump for a bigger jump? gas vs heat pump cost.