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Department for Business, Energy and Industrial Strategy

Retrofit Burner Control Systems

1.1    Scope

Burners are used to provide heat for hot water, steam and thermal oil boilers, heaters and processes. They are widely used in industry and commerce. Traditionally adjustable cams and mechanical linkages have been used to control the fuel valves and air dampers that modulate burner heat output. These mechanisms are susceptible to mechanical wear and hysteresis, and are progressively being replaced by more accurate burner control systems.

A range of retrofit burner control systems is available, and these offer different levels of precision and repeatability of control. The Energy Technology List (ETL) aims to encourage the purchase of microprocessor- based products that are able to accurately control combustion and maintain burner efficiency over a specified turn down range.

As installers assemble retrofit burner control systems on site from standard components from different manufacturers, which reflect the specific requirements of the installation, only the retrofit burner control units are listed on the ETL.

To be eligible for inclusion on the ETL, products shall meet the requirements as set out below.

1.2    Definitions

Retrofit burner control systems are products that are specifically designed to automatically control in an energy efficient manner, the operation of industrial and commercial burners, and the matching of burner heat production with heat demand. 

1.3    Requirements 

1.3.1    Eligibility requirements  

To be eligible, products shall:

  • Incorporate a microprocessor based control system.
  • Be designed to:
    • a)    Control one or more forced draught, gas and/or oil fired burners.
    • b)    Use a precision servomotor to adjust any mechanical airflow dampers and/or modulating gas valves that control the air-fuel ratio of the burners controlled. Each precision servomotor shall be controlled by a positional or flow based feedback mechanism that automatically adjusts its operation to correct for mechanical wear, valve stiction and hysteresis.
    • c)    Where the burners being controlled are gas fired or dual fuelled, use a variable speed motor drive or controller to operate the burners’ forced draught fans.
    • d)    Fully close the air dampers of the burners on shutdown.
  • Automatically respond to changes in heat demand by modulating burner output:
    • a)    In a continuous manner across a minimum specified turndown ratio of 4:1
    • b)    Whilst adjusting the ratio of air and fuel fed to the burner in a manner that maintains combustion efficiency across the required turndown range and complies with the maximum permitted levels of oxygen and carbon monoxide in the burner’s exhaust gases, as set out in Table 1.1.
  • Have an appropriate Conformity Assessment mark, or conform with The Electromagnetic Compatibility Regulations 2016 in respect of their design, manufacturer and testing procedures.

1.3.2    Performance requirements 

Products shall be able to control all categories of burners for which they are designed in a manner that does not exceed the maximum permitted levels of oxygen (O2) and carbon monoxide (CO) in the burners’ exhaust gas at each of test points specified in Table 1.1.

Table 1.1    Minimum performance requirements for retrofit burner control systems

Maximum O2  level at test point

Maximum CO level

100% MCR

50% MCR

25% MCR

All test points





Where MCR is the product’s maximum continuous rating. 

1.4    Measurement and Calculations

1.4.1    Measurement standards

Product performance at the three required test points specified in Table 1.1 (above) shall be determined by fitting the product to an appropriate burner and testing in accordance with the procedures and test conditions in one of the following standards:

  • BS EN 676:2003+A2:2008 “Automatic forced draught burners for gaseous fuels”
  • BS EN 267:2009+A1:2011 “Automatic forced draught burners for liquid fuels”

1.4.2    Calculation Requirements

Where the product’s turndown ratio is greater than the minimum required, performance at the 25% and 50% test points may be calculated by linear interpolation of the test results. Where operation at the burner’s maximum continuous rated output is not possible, performance at the 100% test point may be determined by extrapolation of test data at two additional test points (e.g. 70% and 90%).

1.4.3    Rounding  

For the avoidance of doubt, the oxygen levels in the test burner’s exhaust should be presented to 1 decimal place, and carbon monoxide levels to zero decimal places. As an example, where the test burner’s exhaust gases contain oxygen levels of 3.1% at 100% of the test burner’s maximum continuous rating, or carbon monoxide levels of 21ppmv at any test point, the product application would be deemed to be a fail.

1.5    Verification for ETL Listing 

Any of the following testing routes may be used to demonstrate the conformity of products against the requirements:

  • In-house testing – Self-certified
  • In-house testing – Self-tested and verified or cross-checked by an independent body
  • Witnessed testing
  • Independent testing
  • Acceptance Tests or Field Trials

Further information regarding the first three routes can be found in the ETL Testing Framework.

1.6    Conformity testing

Products listed on the ETL may be subject to the scheme’s conformity testing programme in order to ensure listed models continue to meet the ETL requirements.

1.7    Review 

1.7.1    Indicative review date 

The next technical review is scheduled for 2023-24. 

1.7.2    Illustrative future direction of the requirements  

Future changes to the Specification may include:

  • To consider re-introducing exhaust gas analysers at the time of the next criteria review
  • Absolute value of boiler system efficiency
  • Requirements regarding multi-fuel capabilities (i.e. hydrogen)
  • Introduction of advanced feedback loop category that would incorporate live measurements in control algorithms.