Can I fix Rinnai code 10 myself?

Start with these safe checks: Go outside and make sure the intake and exhaust vent terminals aren't blocked by snow, ice, leaves or nests. Don't touch the exhaust, it can be hot. On a condensing model, check that the condensate drain line where it empties isn't clogged or frozen. Rinnai's internal checks (vent joints, air filter, fan, heat exchanger) are for trained professionals. If you smell gas, leave and call your gas supplier from outside.

When should I call a technician for code 10?

Rinnai's internal checks (vent joints, air filter, fan, heat exchanger) are for trained professionals. 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 10: Air supply or exhaust…

What 10 means

The heater detected an air supply or exhaust blockage. On condensing SENSEI models it can also mean the condensate trap is full because the drain line is clogged or frozen.

Likely causes

Blocked vent terminal (snow, leaves, nests)
Clogged or frozen condensate drain line
Debris in the vent

Safe first checks

Go outside and make sure the intake and exhaust vent terminals aren't blocked by snow, ice, leaves or nests. Don't touch the exhaust, it can be hot.
On a condensing model, check that the condensate drain line where it empties isn't clogged or frozen.

When to stop

Rinnai's internal checks (vent joints, air filter, fan, heat exchanger) are for trained professionals. 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.