Things to consider:

a). Your boiler should be checked on an annual basis by a gas safe registered engineer like a Highgate Plumber . This will guarantee that it will run smoothly and safely. It will also give you peace of mind and guaranteed work with a point of contact should the problem reoccur.
b). Fit a carbon monoxide detector as a minimum action, so at least you have a warning of a leak. If a leak occurs call the National Gas Emergency Service immediately.
c). Never cover or block the air vents on your gas boiler. Always check that any flues on the outside of your property are not blocked off.
d). Operate the central heating system at the very least once a month, even during the summer, this will definitely help to keep it running efficiently and clear the boiler pump of debris and grit that may have gathered when it’s not in use and provide a flow of water through your radiators for flushing.

If you ever suspect a gas leak you must immediately contact the National Gas Emergency Service immediately on 0800 111 999.

*If you are tenant, it is your landlord to arrange for all gas appliances in the property, including the boiler, to be checked annually and he or she must also provide you with a copy of the CP12 Gas Safety Certificate covering:

Gas appliances will be checked for gas tightness. Highgate Plumbers will do this.

If test points are available, standing and working pressure will be tested.

Your Gas Safe engineer will check burner pressure and gas rate against the manufacturers data plate.

Checks will be carried out for the provision of all necessary ventilation.

Flue flow will be tested to make sure products of combustion are removed.

All flame failure devices will be checked for satisfactory operation.

Where appropriate checks will be made for physical stability, presence and effectiveness of stability brackets.

Investigations for any evidence of unsafe operation will be made and reported.

Without completing all of the above checks an appliance cannot be issued a gas safety certificate (CP12).