No hot water

this may indeed be a fault with the boiler but there are things that you can do so that you can have hot water temporarily whilst you wait for the plumber to visit

Do you have a 'combi' or a 'system'?

a combi does not have any storage cylinders. If you have a combi you can try switching off at the power to 'reboot' it. Switch back on and this sometimes will fire it up. If it doesn't re boot report this as a fault. you will probably not have any heating either 

a system

1 check the programmer first - is the thermostat correctlyset

2 check the cylinder stat - this is actually on the cylinder - this can sometimes be knocked by the vacuum or suitcases stored next to it - check that it is on and at temperature ( about 60 degrees)

3. if you have heating but can't get hot water as a temporary measure you can open up the lever at the top of the cylinder - this is a silver box and will allow water to run to both systems- you still need to report a fault

4. you can heat water with the immersion - this is an electric switch close to the cylinder usually with a red light on it or labelled . Again this is a temporary measure so the fault needs to be reported