The answer to 'boiler not heating' is that there are several common causes, including a pilot light issue, thermostat problem, low water pressure, or a malfunctioning boiler component. Symptoms may include the boiler running but not heating, inconsistent heating, or the boiler not turning on at all.
For minor issues like a pilot light or thermostat problem, you may be able to troubleshoot and fix it yourself. However, for more complex problems with the boiler's components, it's best to call in a professional HVAC technician. They can properly diagnose the issue and make the necessary repairs to get your boiler heating efficiently again.