Rinnai code 79: water leak detected

Some Rinnai models have a leak sensor in the bottom of the cabinet. When it gets wet, the unit shuts down and shows code 79 so a small leak does not turn into a big one.

According to Rinnai's diagnostic guide, this code applies to non-SENSEI models.

What to do first

1. Turn the heater off at the controller.
2. Look under and around the unit for water. Check the pipe connections below it, the pressure relief valve and the vent above it.
3. If water is dripping from a connection, close the cold water isolation valve under the heater.

Where the water can come from

• A leaking heat exchanger or internal pipe joint. Rinnai lists these first.
• A loose external connection dripping into the cabinet.
• Condensation or rain entering through the vent.
• A false alarm from a faulty sensor, when no water is found anywhere.

What a technician does

With the cover off, the technician checks the heat exchanger and internal piping, wipes or blows out any water, dries the sensor and restarts the unit. If there is no water but the code persists, the sensor is unplugged as a test. If the heater runs normally without it, the sensor and its screw are replaced.

If the heat exchanger is leaking

A leaking heat exchanger is usually the most expensive repair on a tankless unit. Check whether it is still under warranty, and on an older unit compare the quote with a replacement. Scale and freezing are two common reasons heat exchangers fail, so protect a new one with regular descaling and freeze protection.

See the full list on our Rinnai error codes page.