Code 11 = No ignition. The unit attempted to fire and failed to detect flame. This is the highest-volume Rinnai error code by a wide margin (8,400+ monthly searches), because it has many possible causes.
Diagnostic sequence (in order — cheapest fixes first)
1. Gas supply
- Confirm the gas valve at the unit is fully open
- Test another gas appliance in the house — if all gas appliances are out, the issue is utility supply, not the heater
- Check propane tank level if LP — running low LP throws Code 11 reliably
2. Air in the gas line
If the gas was recently turned off (new install, repair work, utility outage), the line has air. Purge by running another gas appliance for 5-10 minutes, then attempt Rinnai restart.
3. Gas pressure
Rinnai needs minimum 4" WC inlet pressure on natural gas, 10" WC on propane, sustained during fire. Undersized gas line is the #1 chronic cause of Code 11. A licensed plumber tests this with a manometer. See gas line sizing.
4. Flame rod (the #1 hardware cause)
The flame rod (also called flame sensor) detects flame via micro-current. Carbon buildup or corrosion drops its signal below the controller's detection threshold. Cleaning the flame rod with fine sandpaper resolves about 40% of chronic Code 11 cases. See our flame rod page.
5. Igniter
Direct spark igniter wears out. Check for spark when the unit attempts to fire (dark room, look through the sight glass). No spark = igniter or igniter cable. See igniter page.
6. Gas valve
Less common but does happen. Gas valve solenoid stuck closed — replace assembly. Dealer-installed only.
Reset procedure
- Address the suspected cause from the sequence above
- Press On/Off on the controller (Level 1 reset)
- If code returns immediately, escalate to next cause
- If code clears and unit runs normally, monitor for 24 hours
Common scenarios
- Code 11 only at high flow: gas line undersized — Code 11 throws when modulation demands full burn
- Code 11 after cold snap: propane tank pressure dropped — tank too small or regulator iced
- Code 11 after install: air in line, undersized line, or no gas pressure test was performed
- Code 11 in old unit (10+ years): flame rod or igniter end-of-life — both are routine replacements
Bottom line
Work the diagnostic sequence top-down. Flame rod cleaning is free and resolves a huge fraction of cases. If you've tried steps 1-4 and the code persists, call Rinnai support at 1-800-621-9419.