Water heater shuts down and displays error code 10; unit may run briefly then stop, often during high-demand usage.

Safety first: Turn OFF gas at the manual gas shutoff valve and switch OFF electrical power to the heater before inspecting. Do not operate the unit with the front cover removed.

Steps to check and correct:

• Inspect vent termination: Go outside and locate the Noritz vent termination. Make sure it is not blocked by snow, leaves, bird nests, or debris. Clear any obstruction and ensure at least the minimum clearance specified in the Noritz installation manual from walls, soffits, and other structures.
• Check intake air screen (if applicable): On direct-vent Noritz models, remove the intake air screen at the vent collar and clean off dust, lint, or spider webs using a soft brush or vacuum. Reinstall securely.
• Verify venting configuration: Compare your vent length, number of elbows, and pipe diameter to the Noritz venting chart in the installation manual. Excessive length or too many elbows can cause error 10. If the run is out of spec, shorten or reconfigure the venting. Use only approved vent materials (e.g., Category III stainless or manufacturer-approved concentric vent).
• Check for sagging or back-pitched vent: Ensure horizontal vent sections are properly supported and pitched per Noritz specs (typically upward toward the termination). Correct any low spots where condensate can pool.
• Reset and test: Restore power and gas, then run hot water at a fixture. If error 10 returns after clearing obstructions and verifying venting, contact a qualified Noritz technician to check the combustion fan and pressure switch.