Get your gas appliances checked every year by a professional installer, preferably registered with CORGI (the Confederation for the Registration of Gas Installers). In addition, you can take these steps at any time to ensure safety.
Run the dust-brush attachment of your vacuum cleaner over the louvred access panel of the ventilator to remove accumulated dust and fluff particles. Ventilators and flues must not be blocked or obstructed, because the waste products formed by gas burning need to escape; if they do not they will build up and eventually poison you.
If you have a gas fire fitted into a fireplace, get the chimney swept every year to clear it of any blockages. This must also be done before the gas fire is fitted.
If you notice any sooty deposits or staining around a gas fire or heater, call a competent installer to check it.
Buy second-hand gas appliances only if they have been certified for safety and the dealer gives you a written guarantee. Make sure there is a copy of the user's instructions with any cooker that you buy. Second-hand appliances should be installed only by a professional fitter - from British Gas or some other person registered with CORGI.
Never fit gas appliances yourself.