Water heater will not ignite; display shows error code 11; no hot water at any fixture.

Safety first: Turn OFF power to the heater and close the manual gas shutoff valve. If you smell gas, evacuate the area and contact your gas supplier or emergency services.

Steps to check and correct:

• Verify gas supply: Confirm the gas shutoff valve to the Noritz unit is fully open. If other gas appliances are also not working properly, contact your gas utility. For LP systems, ensure the tank is not empty and the regulator is functioning.
• Check gas line sizing: Compare the gas pipe size and length to the Noritz installation manual. Undersized piping can cause low pressure and error 11 under load. This typically requires a licensed plumber to correct.
• Inspect igniter: Remove the front cover (after power is off). Locate the igniter assembly near the burner. Check for cracks, heavy carbon buildup, or loose mounting. Gently clean the ceramic and tip with a soft brush; do not sand or bend the electrode. Re-secure the igniter.
• Check ignition wiring: Inspect the igniter wiring harness from the PCB to the igniter for loose connectors, burn marks, or damage. Reseat connectors firmly.
• Reset and test: Restore gas and power. Open a hot water tap and observe. If error 11 persists, the gas valve assembly or control board may be faulty and should be tested and replaced by a qualified Noritz technician.