What does error code 11 mean on a Rinnai tankless water heater?

No ignition. The heater tried to light and couldn't.

Can I fix Rinnai code 11 myself?

Start with these safe checks: Make sure the gas valve to the heater is open and, for propane, the tank has fuel. Check whether other gas appliances are working, which points to a supply problem. Gas pressure, igniter and flame rod checks are for a qualified gas technician. If you smell gas, leave and call your gas supplier from outside.

When should I call a technician for code 11?

Gas pressure, igniter and flame rod checks are for a qualified gas technician. If you smell gas, leave and call your gas supplier from outside. Smell gas? Leave right away, don't touch light switches or phones inside, and call your gas utility or 911 from outside. Never open a gas valve, burner, gas line, vent or flue connection, or bypass a safety switch. Repeated lockouts, scorching, soot, or a CO alarm mean shut it off and call a licensed gas technician.

Rinnai Tankless Water Heater Error Code 11: No ignition

What 11 means

The heater tried to light and couldn't.

Likely causes

Gas valve closed
Empty propane tank
Air in a new gas line
Low gas pressure
Igniter or flame rod problem

Safe first checks

Make sure the gas valve to the heater is open and, for propane, the tank has fuel.
Check whether other gas appliances are working, which points to a supply problem.

When to stop

Gas pressure, igniter and flame rod checks are for a qualified gas technician. If you smell gas, leave and call your gas supplier from outside.

Checked against: Rinnai: Troubleshooting Tankless Water Heater Diagnostic Codes (100000652). Codes can differ by model and year, so confirm with your owner's manual.