The answer to 'why is my boiler blowing cold air' is that there are several common causes, including a malfunctioning thermostat, low water pressure, or a problem with the boiler's heating element or circulator pump. Symptoms may include the boiler running but not heating the home, or the radiators or vents blowing cold air.
Some potential solutions include checking the thermostat settings, ensuring the boiler has adequate water pressure, and inspecting the heating components for any issues. However, if you're not comfortable troubleshooting the problem yourself, it's best to call in a professional HVAC technician to diagnose and repair the issue.