Furnace indicates a gas valve or modulation fault; burner may stay at minimum or not light at all.

Safety first: Turn off gas and power. Only qualified personnel should adjust or replace gas valves.

• Visual inspection: Locate the gas valve on the Sime furnace gas train. Check for signs of overheating, corrosion, or physical damage.
• Check connectors: Ensure the electrical plug(s) on the gas valve are firmly seated. Inspect wires for cuts or burns.
• Verify supply pressure (technician): A manometer is required to check inlet and outlet gas pressures. Do not attempt this without training.
• Reset furnace: After confirming wiring, restore gas and power and reset the unit. If the error persists, the gas valve or control board likely needs replacement and combustion must be re‑commissioned by a Sime‑approved technician.