The answer to 'why is my boiler not heating' is that there could be several common causes, such as a malfunctioning thermostat, low water pressure, a blocked or dirty air filter, or a problem with the boiler's internal components. Symptoms may include the boiler not turning on, the home not getting warm enough, or strange noises coming from the boiler.
Some potential solutions include checking the thermostat settings, ensuring the boiler has adequate water pressure, cleaning or replacing the air filter, and inspecting the boiler for any visible issues. However, if the problem persists or you're not comfortable troubleshooting the boiler yourself, it's best to call a professional HVAC technician to diagnose and repair the issue.