Error 12 appears on the Richmond tankless display; burner lights briefly then goes out and unit shuts down.

Safety first: Turn OFF power and gas. Flame sensing issues can be related to combustion problems—ensure adequate ventilation.

• Clean flame rod: Remove the front cover and locate the flame rod (often combined with the igniter on some models). Gently clean the rod with fine abrasive pad to remove oxidation. Do not bend or crack the ceramic.
• Check ground connection: Verify that the heater's ground wire is securely attached to the chassis and that the electrical supply has a proper ground. Loose grounds can cause flame sensing errors.
• Inspect venting: Check intake and exhaust for obstructions and verify correct installation. Poor venting can cause the flame to lift or blow out.
• Monitor gas supply: If other gas appliances flicker or go out, contact a gas technician to check supply pressure and regulator operation.
• Service gas valve if needed: If cleaning and vent checks do not resolve error 12, a professional should test and possibly replace the gas valve or control board.