Furnace runs but produces no heat, blower runs with cold air

Safety first: Turn off power and gas if you smell gas. Do not use open flames to test for leaks.

• Step 1 – Thermostat check: Ensure the thermostat is calling for heat and the setpoint is above room temperature.
• Step 2 – Gas valve position: Confirm that the manual gas shut‑off near the furnace is fully open.
• Step 3 – Other gas appliances: Check if other gas appliances work. If not, contact your gas supplier.
• Step 4 – Observe ignition: If safe, watch through the inspection window during a call for heat. If there is no spark or flame, the ignition or gas valve may be faulty and should be checked by a technician.