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Boiler Service

A practical maintenance checklist for heating professionals. Tick items as you work through a service — your progress is saved in this browser until you clear it.

A modern boiler is often an electromechanical appliance with several moving parts and system components that can break down when you least expect. The checks below form a general maintenance schedule for boiler servicing.

In Europe, boilers may be maintained on hours-used (similar to cars) or on a time schedule — annual or biennially. In the UK we typically work to an annual maintenance schedule. Many manufacturers also invalidate extended warranties if the boiler is not serviced annually.

Checklist for modern condensing boilers

Combustion performance analysis / emissions testing

Most modern boilers require checking their combustion ratios using a flue gas analyser (FGA). Many older non-condensing boilers can also be checked using an FGA. Some older boilers in which you cannot measure combustion performance will require full strip down and servicing. The following CO/CO2 ratio levels trigger actions:

CO / CO2 ratio Action required
0.0040 and lower Does not require any further action
0.0040 to 0.0080 Requires cleaning
0.0080 and above Requires full investigation and overhaul — classed as immediately dangerous

Example calculation

Data: CO 10 PPM, CO2 9.0%

  1. Convert CO2 to PPM: 9.0 × 10,000 = 90,000 PPM
  2. Ratio = 10 ÷ 90,000 = 0.0001

Key: PPM = parts per million.

Other information

There are other checks that are important and should be carried out by engineers. Checking the water quality of the heating system is crucial for a long-lasting system. Making sure correct levels of inhibitor / protector will help ensure the system does not corrode internally and cause premature breakdown of parts. Checking other parts of the system can indicate problems that may be caused by the boiler or to the boiler.

Information is guidance only; repairs require qualified professionals. Do your own due diligence; we accept no liability.