Work Performed: Verified previous replacement of both primary and secondary heat exchangers on a 1-year-old furnace. Performed full diagnostic and combustion test to confirm system performance and gas flow stability. - Measured gas inlet pressure: 7.2" WC static, 6.68" WC under load — both within manufacturer specifications - Verified inlet pressure stability during a 10-minute burner operation test - Checked manifold outlet pressure: 3.2" WC — stable throughout firing cycle - Removed all burners, inspected, and cleaned ports; verified proper alignment and correct orifice size - Removed and cleaned brass orifice fittings at gas valve manifold to ensure unobstructed gas flow - Inspected secondary drain trap and venting for residual water or blockages - Performed combustion analysis after 10-minute runtime; ran system with intake both connected and disconnected to compare oxygen and CO readings - Initial readings showed low oxygen, but final readings stabilized around