What does error code 12 mean on a Rinnai tankless water heater?

Flame failure. The flame lit but was lost.

Can I fix Rinnai code 12 myself?

Start with these safe checks: Make sure the gas valve is fully open and, for propane, the tank isn't low. Check outside that the vent terminals aren't blocked. Flame rod, gas pressure and burner checks are for a qualified gas technician.

When should I call a technician for code 12?

Flame rod, gas pressure and burner checks are for a qualified gas technician. 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 12: Flame failure

What 12 means

The flame lit but was lost.

Likely causes

Low or interrupted gas supply
Propane running low
Dirty or loose flame rod
Venting problem

Safe first checks

Make sure the gas valve is fully open and, for propane, the tank isn't low.
Check outside that the vent terminals aren't blocked.

When to stop

Flame rod, gas pressure and burner checks are for a qualified gas technician.

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