What does Rinnai error code 79 mean?

Rinnai titles code 79 Water Leakage Detected. Its diagnostic manual lists it for the non-SENSEI series. The SENSEI series sections of the same manual do not list code 79, so if you have a newer SENSEI model the code you see may be different. Check the model on your rating plate against the manual.

What triggers it is a leak detector inside the cabinet. When it sees water, the heater shows the code and stops. Water is the obvious cause, but the detector, its wiring and its screw are also parts that can fail, and Rinnai's checklist has a step to tell the two apart.

Rinnai lists four steps, and their order tells the story:

1. 1Check the wiring at the leak detector for loose, broken or damaged wiring or connections.
2. 2Check the heat exchanger and all the piping inside the water heater for leaks.
3. 3If no leaks are found, inspect the cabinet for water pooling on the bottom pan. Wipe or blow out any water found. Dry off the leak sensor and restart the water heater.
4. 4If no water is found in the cabinet, unplug the sensor and fire the water heater. If the heater operates with the sensor unplugged, replace the sensor and its screw.

Notice that the first thing Rinnai asks is whether the sensor is wired correctly, and the last is whether the sensor itself is bad. Everything in between is looking for water. That sequence is deliberate: a real leak comes first in importance, but a damp sensor or a bad connection is common enough to have its own steps.

### Where could the water be coming from?

Rinnai's steps mention the heat exchanger and internal piping. Rinnai's installation manual describes several other places water can reach the cabinet floor:

• The pressure relief valve. The manual says the valve must be piped to a safe drain, and that it must be operated manually once a year. Rinnai warns that water discharged from this valve can cause severe burns or scalds, so a valve that is discharging is a reason to keep everyone back and call a professional.
• The condensate drain. A condensing unit produces water as it runs, and it has an integrated trap and a drain line. A drain line that has come loose or backed up can spill inside the cabinet. Our page on Rinnai error code 25 covers what a good condensate drain looks like.
• The plumbing connections at the bottom. The hot and cold connections, the isolation valves and the inlet filter are all on the water side, and any of them can weep. Rinnai's manual says the inlet filter is cleaned by closing the isolation valves and removing it, so a recently serviced filter is a connection worth checking.
• A leaking heat exchanger. This is the one that needs a technician. Rinnai's warranty section excludes scale build up and freeze damage among other causes, so a heat exchanger leak can become a replacement decision. Our page on how often to descale a tankless heater in Phoenix explains how scale builds.

Start with the gas smell rule, because a tankless heater is a gas appliance. If you notice a gas odor near the unit, get everyone out, keep away from light switches, and call Southwest Gas at 877-860-6020 or 911 once you are outside.

With no gas smell:

1. 1Look for water on the floor, under the heater and inside a garage or closet. Note whether it is a few drops or a puddle, and whether it is cold or hot.
2. 2If you see water coming from the heater, close the water supply to it. The isolation valves on the hot and cold lines, if the heater has them, are the quick way. Otherwise shut off the water at the main. Then turn the heater off.
3. 3Do not open the cabinet if the heater is wet inside. Rinnai's manual says to turn off power, gas and water before servicing, and water near live parts is a reason to wait for a professional.
4. 4If everything is dry, note that the code may be the sensor. Rinnai's third step is to dry the sensor and restart. Rinnai's manual limits its service instructions to trained and qualified professionals, so leave that one to a technician.

A test that anyone can do is the one the EPA describes for finding a hidden leak in the house. Read your water meter, wait two hours with no water in use, and read it again. If the meter has changed, you probably have a leak somewhere. It does not tell you the leak is at the heater, but it tells you whether a leak exists at all. If the meter moves and the heater is dry, the leak may be elsewhere in the plumbing, and our page on the signs of a slab leak in Arizona covers what to look for next.

### Should I keep using the heater?

No, not until the source is found. A heater that has detected water has shut itself down for a reason. Even if the sensor turns out to be the problem, Rinnai's fourth step runs the heater with the sensor unplugged as a test, which is a technician's diagnostic, not an operating mode. Use another source of hot water if you can, and keep the supply off if there is any sign of dripping.

### What should I tell the technician?

A few facts speed up the diagnosis. Say whether the heater is in a garage, a closet or outside, since exposure and dust affect a sensor. Say when the code first appeared and whether it followed rain, a water shutoff, or service on the heater or the plumbing near it. Say whether you saw any water, and where. And say what the code did after you dried the area, if you did: a code that vanishes and returns points to a real slow leak or a damp sensor, while a code that stays with a dry cabinet points to the sensor or its wiring.

Call for any code 79 with visible water, any wetness inside the cabinet, any leak that comes back after you dry it, or a heater that will not restart. Call right away if the leak is active, if the floor around the heater is wet, or if you smell gas. Water damage spreads to drywall and flooring the longer it runs, so an early call limits the damage.

HQ Plumbing and Air is licensed and insured, and we answer emergency calls 24/7. Free estimates and upfront pricing come standard. For the complete list of codes, see the Rinnai tankless code list. Our page on a water heater drain pan that overflows covers what to do when water reaches the pan.