The answer to 'why is my boiler not working' is that there could be several common causes, such as a lack of fuel, a faulty thermostat, low water pressure, or a problem with the pilot light or electrical components. Some common symptoms include the boiler not turning on, not heating up properly, or making unusual noises.
If the boiler isn't turning on at all, check that the fuel supply (gas or oil) is on and that the pilot light is lit. If the pilot light is out, you may be able to relight it yourself, but if it keeps going out, there could be an issue with the gas valve or thermocouple that requires professional repair. Low water pressure can also prevent the boiler from firing up, so check the pressure gauge and add more water if needed.