Your boiler is failing to light the gas flame, which means you currently have no heating or hot water.

DIY fix possible

Check if your gas meter has credit (if prepay) or if other gas appliances like your hob are working.Press and hold the 'Reset' button for five seconds to see if the boiler restarts.If it is freezing outside, check if the white plastic condensate pipe leading outdoors is frozen and thaw it with warm water.