Illustration of a small water-leak sensor placed on the floor near a tankless water heater, next to a drain hose.

Rinnai Code 79 (Water Leak Detected)

by

Rinnai code 79 means the built-in leak sensor detected water inside the unit and shut it down as a safety measure. It’s sometimes a real leak, but there’s a documented false-alarm cause tied to condensation and a leak-detection sensor screw set too long, per a Rinnai technical bulletin referenced in owner forum threads.

Illustration of a small water-leak sensor placed on the floor near a tankless water heater, next to a drain hose.
Illustration of a small water-leak sensor placed on the floor near a tankless water heater, next to a drain hose.

Likely Causes, Ranked

  1. Actual water leak inside the case
    From a fitting, the heat exchanger, or a condensate line.
  2. Condensation misread as a leak
    Normal condensate can trigger the sensor if it collects in the wrong spot.
  3. Leak-detection sensor screw set too long
    A Rinnai tech bulletin, cited in a diychatroom forum thread, identifies this specific fix for nuisance code 79 trips.

Step-by-Step Diagnosis

  1. DIY SAFE
    Turn off the water and power to the unit

    If you see standing water anywhere in or around the case, don’t power it back on yet.
  2. DIY WITH CAUTION
    Open the case and look for the actual water source

    Fitting, connection, or condensate line — photograph what you find.
  3. PRO ONLY
    If no leak is visible, check the leak-detection sensor screw

    Per the Rinnai tech bulletin referenced in owner reports, a screw set too long can trigger false leak detection. This is a precise adjustment — verify against your model’s service bulletin before touching it.
  4. PRO ONLY
    If you find a real leak

    Don’t reset and run the unit again until the leak is fixed. Running a tankless unit with an active leak near the electronics is a real hazard.

FAQ

Is Rinnai code 79 always a real leak?

No — there’s a documented false-alarm cause from a leak-sensor screw adjustment, referenced in a Rinnai technical bulletin. But treat every code 79 as a real leak until you’ve actually looked inside the case.

Written by HotWater Decoded — water heater repair specialists. Technically reviewed by a licensed technician on our team.

Sources

  • diychatroom.com forum thread citing a Rinnai technical bulletin on nuisance code 79

Home · About · Contact ·
Privacy Policy · Terms & Conditions ·
Disclaimer · Editorial Policy
© 2026 HotWater Decoded. All rights reserved.