No hot water?

I have hot water which only lasts for seconds then my bolier fails to fire up again to give me constant hot water. I have a baxi bolier and it is only 3 yrs old. There are no light flashing to indicate a problem with the boiler, as it should. This has suddenly just happened over night with no repairs or work done to anything. Is this a major problem or can i fix it myself?It appears that theres no message getting to the boiler to tell it to re-fire to keep constant hot water.