The answer to 'preventive maintenance not heating' is that there are several common causes for a heating system not working properly, even with regular maintenance. Potential issues include a dirty air filter, malfunctioning thermostat, broken heating element, or problems with the furnace or boiler itself.
Symptoms may include the system not turning on, poor airflow, uneven heating, or higher energy bills. Homeowners can try simple DIY troubleshooting like changing the air filter, but for more complex issues it's best to call in a professional HVAC technician to diagnose and repair the problem.