Boiler Efficiency Ratings

Compare new boilers and assess whether your current boiler would be better off being replaced

Our boiler efficiency tables provided by SEDBUK (the seasonal efficiency of domestic boilers in the UK) provide a guide of how effective your boiler is at turning fuel into heat.

You can check your boilers rating by selecting it’s make and model below. Ratings are based on the SEDBUK Rating which is an indicator of its efficiency when used within an average domestic household, it’s a great benchmark for comparing new boilers and also assessing whether your current boiler would be better off being replaced due to low efficiencies.

For new boiler installations call British Gas Boilers on 0333 230 5216 for a no-obligation quote, alternatively visit Boiler Guide to request quotes from independent local and regional heating engineers.



Heatslave 2 g40bf Efficiency

SAP seasonal efficiency


Rating band



ManufacturerWorcester Boilers
ModelHeatslave 2 g40bf
Fuel TypeGas
Flue TypeRoom-Sealed
FanNo Fan
Output (kW)11.72 - 11.72
Boiler ID4131113
Manufactured From/ToUnknown - 1984


The Worcester Heatslave 2 g40bf is unrated, this probably means it's obsolete or very old.

The Heatslave 2 g40bf is a Non-Condensing Conventional boiler with a maximum power output of 11.72kw that uses Gas as its fuel source.

Being an Unrated boiler it would be worthwhile replacing it with a higher efficiency 'A' rated boiler.


Similar Worcester Boilers to the Heatslave 2 g40bf
(Non-Condensing Gas Conventional)

Results ordered by efficiency. Some models may be obsolete.

Worcester 14/19 CBi RSF

79.4% Efficient

Worcester 15 Sbi RSF

79.1% Efficient

Worcester 9/14 CBi RSF

78.5% Efficient

Worcester 19/24 CBi RSF

78.4% Efficient

Most Efficient Conventional Gas Boilers

Baxi Solo 15 HE A

91.3% Efficient

Main 15 HE A

91.3% Efficient

Potterton Promax SL 15

91.3% Efficient

Potterton Gold H 15

91.3% Efficient