It is all about checking that the boiler has been installed to the manufacturer’s and British Standards and it is still in a satisfactory condition for continued safe use.
The engineer will do the following checks:
The Flueway - the pipe or pipes leading from the boiler that contain the fumes from the boiler, also known as the chimney.
Check the seals that prevent the fumes from entering the building.
Check the ventilation that is required for the appliance to work safely.
Check the condition and the route of the chimney or flue.
Gas supply - the pipe supplying the flammable gas to the appliance
Check the gas supply is not leaking and that it is fitted in such a manner that it is not likely to leak in the future.
Check the valve that is in the appliance to ensure it works correctly and allows the right amount of gas into the appliance and switches off when it should.
Electrical supply - the wires that supply the appliance with electricity.
Check that the electrical flex leading to the appliance is in good condition.
Check that the fuse fitted to protect the appliance is of the correct size and type.
Check that the controls that switch the boiler on and off are as designed.
Check if there are better controls available to reduce the amount of energy used
Combustion - the way the gas burns.
Check that the appliance is burning the gas correctly and not producing higher than allowed levels of carbon monoxide or carbon dioxide and that the ratio between the two is within allowable tollerances for that appliance.
Condense drain - the pipe that may get the waste product to drain after efficient combustion.
Check that the amount of acidic water being produced can be taken away to a safe drain properly without the possibility of freezing in cold weather.
The engineer will then advise you of any defects or poor results in writing with a course of remedial action.
What a gas service engineer does when servicing an appliance.