If you live on the ground floor it is likely that your boiler is not working because the condense pipe is frozen. This is will be a plastic pipe leading from the boiler through the wall to outside of the property.
To remedy this pour warm water (not boiling water) over the section of the pipe outside your home from a jug or watering can. Alternatively you can lay a hot water bottle directly onto the pipe. This can unfreeze the pipe and get your the boiler working again.
The boiler may need to be re-set once the condense pipework has been defrosted.
British Gas have made short video explaining this process which can be viewed here:
Watch the video
If you are council tenant and are not able to do this please contact our heating repairs contractor for assistance: