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Benchmark - New CO testing procedures come into Force

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New Procedure


Following concerns arising from a very small number of carbon monoxide (CO) incidents involving condensing boilers, the Heating and Hotwater Industry Council (HHIC), with the collaboration of members and associated organisations, has developed a procedure for checking and recording CO level and combustion ratio (CO/CO2) in the boiler flue gas as part of the commissioning process. 

Boiler manufacturers despatch all appliances with the combustion settings precisely set to tolerance. Therefore when the appliance has been installed to the manufacturer's installation instructions there is no need for adjustment of the air/gas ratio valve during the installation and commissioning procedure. However they do not have any control over the integrity of the flue to which the boiler is attached, or of other situations which may arise during installation. For this reason it has been agreed that at the end of the commissioning process a final ECGA check of flue gas CO level and combustion ratio must be carried out. 

It is important to note that the procedure is intended as a simple commissioning check and does not apply to service or maintenance activities involving adjustment of the air/gas ratio control valve. 

The checking procedure, which will shortly be published by Gas Safe Register as a new Technical Bulletin (TB), is illustrated in the form of a flowchart, designed to ensure that ECGA measurements are carried out in a consistent and technically correct manner so that accurate readings are obtained for recording purposes. The TB and flowchart are intended as a generic guide, however all HHIC boiler manufacturers have agreed that they will also form the basis of guidance given in their own installation instructions. The boiler manufacturer's instructions must be followed if available.

In the absence of these instructions, manufacturers have agreed that the action levels given in the TB - flue gas CO level less than or equal to 350ppm AND Combustion Ratio less than or equal to 0.0040 - will ensure that the installation can be considered safe.

Revised Benchmark Commissioning Checklist


Assuming they are within expected limits, CO level and combustion ratio must be recorded on the Benchmark Commissioning Checklist provided with every new boiler. This will give both the customer and the installer confidence (and evidence) that the heating system has been left in a safe and efficient working condition. 

HHIC boiler manufacturers have agreed that completion of the Benchmark Commissioning Checklist is regarded as a condition of manufacturer's warranty - hence failure to record CO level and combustion ratio on commissioning may affect warranty provision for the customer. 

Gas Safe Register will defect an installation for Building Regulations non-compliance if CO and combustion ratio are not correctly recorded on the commissioning documentation.

HHIC will shortly issue a revised version of the Checklist with a formal requirement to record CO and combustion ratio. This version will be used by all HHIC boiler manufacturers from April 2014 - at which time the measurement and recording of CO and combustion ratio on commissioning will be a requirement. From April 2013 it is a recommendation that existing Benchmark Checklists should be used for recording purposes.

Further Information

New Gas Boiler Benchmark Checklist

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