1. Check your thermostat
Sometimes a faulty thermostat can throw a spanner in the works. If you suspect all is not well – here's what you should do:
Firstly, set your thermostat to 21 degrees to increase the temperature on the thermostat to see if that triggers the boiler. If this doesn’t work, try putting your heating on full for a little while.
Check that your thermostat settings haven't changed due to an accidental knock. If nothing's changed and the time is set as you expected, it might be time to replace it. A qualified professional can do this for you.
Considered going smart with your heating? You can control temperature and timings, even when you're not at home.