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

The Energy Saving Trust estimates a typical UK household replacing a G-rated non-condensing boiler with a new A-rated condensing combi saves GBP 200 to GBP 580 per year on gas bills. The exact figure depends on house size, current bill, and how the system is used. A 1-bed flat saves toward the lower end (GBP 200-GBP 300); a 4-bed detached toward the upper end (GBP 450-GBP 580). Cumulative savings over the 12-15 year life of a new A-rated boiler can total GBP 2,400 to GBP 8,700, often exceeding the replacement cost.

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 / May 2026

Boiler efficiency ratings UK

Replacing a G-rated boiler (pre-1990s typical) with a modern A-rated condensing combi saves GBP 200-GBP 580 per year on gas bills (Energy Saving Trust UK 2026). Cumulative savings over the 12-15 year life of a new boiler often exceed the install cost.

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. Replacement pays back in 4-7 years on gas savings.

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%Pre-1980s back boilers typical. Replace urgently; GBP 200-GBP 580 annual saving available.

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 2026 figures, assuming UK average gas usage and unit cost:

Current boiler band	Annual saving (semi-detached)	Cumulative 12-year saving
G-rated (pre-condensing)	GBP 480 - GBP 580	GBP 5,800 - GBP 7,000
F-rated	GBP 380 - GBP 480	GBP 4,600 - GBP 5,800
E-rated	GBP 280 - GBP 380	GBP 3,400 - GBP 4,600
D-rated	GBP 200 - GBP 280	GBP 2,400 - GBP 3,400
C-rated	GBP 120 - GBP 200	GBP 1,400 - GBP 2,400

Cumulative figures use a 12-year boiler life and assume flat UK gas pricing. Real cumulative savings rise faster if gas prices rise over the period (as forecast in DESNZ outlooks).

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. GBP 250-GBP 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 (GBP 400-GBP 600) and loft top-up (GBP 200-GBP 400) typically save more per year than the boiler upgrade itself.
Hot water cylinder jacket: GBP 20-GBP 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?

GBP 200-GBP 580 per year on gas bills depending on house size (Energy Saving Trust). Cumulative 12-year saving GBP 2,400-GBP 7,000.

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?

Top of the range models (Viessmann Vitodens 200-W, Worcester Bosch Greenstar 8000 Life, Vaillant ecoTEC Plus with Green iQ) hit 94% seasonal efficiency. The marginal cost of premium efficiency over a standard A-rated combi is typically GBP 400-GBP 800 - pays back over the boiler's life but not before 5-8 years on energy savings alone.

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.