Daikin gas furnace will not start; control board shows U0, inducer may start briefly then stop, no ignition.

Safety first: Turn off electrical power to the furnace and close the gas shutoff valve before touching any gas components. If you smell gas, evacuate and contact your gas supplier or a licensed technician immediately.

Steps to check:

• Verify gas shutoff: Locate the manual gas shutoff valve near the furnace. Ensure the handle is parallel to the gas pipe (open). If perpendicular, turn it slowly to the open position.
• Check other gas appliances: Confirm that other gas appliances (stove, water heater) in the home are working. If they are not, the issue may be with the building gas supply and not the furnace.
• Inspect gas line to furnace: Look for obvious kinks, crushing, or damage to the flexible gas connector feeding the Daikin furnace gas valve.
• Reset power: Restore power to the furnace, then turn the thermostat to HEAT and raise the setpoint. Observe if the U0 code clears after a power cycle.
• Check inlet gas pressure (pro only): A licensed technician should connect a manometer to the inlet test port on the Daikin gas valve and verify pressure matches the rating plate. Incorrect pressure indicates a supply or regulator problem.

Do not attempt to disassemble or replace the gas valve yourself unless you are qualified. Gas valve replacement and pressure adjustment must be done by a licensed HVAC technician.