Code 11 = No ignition. The unit attempted to fire and failed to detect flame. The highest-volume Noritz error code.
Diagnostic sequence
1. Gas supply
- Confirm the gas valve at the unit is fully open
- Test another gas appliance — if all are out, utility supply issue
- Check propane tank level if LP — low LP throws Code 11 reliably
2. Air in the gas line
If gas was recently turned off (new install, repair, utility outage), the line has air. Purge by running another gas appliance for 5-10 minutes.
3. Gas pressure
Noritz needs minimum 4" WC inlet on natural gas, 10" WC on propane, sustained during fire. Undersized gas line is the #1 chronic cause. See install guide for proper gas line sizing.
4. Flame rod (the #1 hardware cause)
The flame rod detects flame via micro-current. Carbon buildup drops the signal below threshold. Cleaning the rod with fine sandpaper resolves about 40% of chronic Code 11 cases. See flame rod page.
5. Igniter
Direct spark igniter wears out. Check for spark when the unit attempts to fire (dark room, sight glass). No spark = igniter or igniter cable. See igniter page.
6. Gas valve
Less common. Stuck-closed solenoid; replacement is dealer-only.
Reset procedure
- Address the suspected cause
- Press On/Off on controller (Level 1 reset)
- If code returns immediately, escalate
- Monitor for 24 hours
Common scenarios
- Code 11 only at high flow: gas line undersized — code throws when modulation demands full burn
- Code 11 after cold snap: propane tank pressure dropped
- Code 11 after install: air in line, undersized line, or no gas pressure test
- Code 11 in old unit (10+ years): flame rod or igniter end-of-life
Bottom line
Work the diagnostic sequence top-down. Flame rod cleaning is free and resolves a meaningful fraction of cases. Persistent code = call Noritz support at 1-877-986-6748.