The answer to 'furnace repair not heating' is that there are several common causes, including a malfunctioning thermostat, clogged air filters, problems with the furnace's heating element or blower motor, or issues with the fuel supply. Symptoms may include the furnace not turning on at all, blowing cold air, or making strange noises.
Many minor furnace issues can be addressed through DIY troubleshooting and maintenance, such as replacing air filters or resetting the thermostat. However, more complex problems like malfunctioning components or issues with the fuel supply often require a professional HVAC technician to diagnose and repair.