Status: Callback Resolved. Issue: Furnace non-operational, Thermostat calling for heat but no ignition. Findings & Diagnostics Initial Assessment: Upon arrival, the system was unresponsive despite a demand for heat from the thermostat. Thermostat Inspection: Verified wiring integrity at the thermostat sub-base. After reseating the unit, the furnace initiated the startup sequence. Ignition Failure: The hot surface ignitor glowed as intended, however, the gas valve failed to open, resulting in a lockout. Fault Isolation: Diagnosed a loose connection at the gas valve. By securing and manipulating the wiring harness, the gas valve successfully opened. Testing: Verified that the gas valve received steady, correct voltage. Manometer testing confirmed stable gas pressures with no significant fluctuations during operation. Resolution: The system was cycled multiple times to ensure reliability. The furnace operated correctly in both Stage 1 and Stage 2 heating modes without furt