Since 2015, all new gas boilers must display an ErP (Energy-related Products) energy label — similar to the energy labels on white goods. Here's how to read it.
The efficiency rating
The large letter grade (A++ down to G) represents seasonal space heating efficiency. Most modern condensing boilers achieve an A rating (90%+) or A+ (98%+). If you see a G-rated boiler for sale, it's not compliant for new installations.
The seasonal efficiency percentage
Below the grade letter, you'll see a seasonal space heating efficiency percentage (e.g., "94%"). This is the ErP efficiency figure — how efficiently the boiler converts gas to heat over a typical heating season.
The hot water class
For combi boilers, there's also a domestic hot water efficiency class. This rates how efficiently the boiler heats domestic hot water — typically A or B for modern combis.
The ErP pack
If you buy a boiler and controls as a system (boiler + smart thermostat), the combined ErP rating can reach A++. This is why fitting a quality smart thermostat improves the overall package efficiency rating.
What it means in practice
A+ vs A efficiency is approximately a 3–4 percentage point difference (e.g., 95% vs 92%). On a £1,100 gas bill, that's about £33/year in savings. Worth the premium on a boiler intended for 12+ years of service.