The answer to 'system upgrade not heating' is that there could be several common causes, including incorrect system sizing, improper installation, or issues with the thermostat or other components. Symptoms may include the system running but not producing enough heat, uneven heating throughout the home, or the system shutting off prematurely.
Some potential solutions include checking the thermostat settings, inspecting the air filters, and ensuring the system is properly sized for the home. However, if the issue persists or you're unsure of the cause, it's best to call a professional HVAC technician to diagnose and repair the problem. Attempting to fix a complex heating system issue without the proper expertise can be dangerous and may lead to further damage.