The short answer
A Rinnai tankless shows its code on the controller, usually a two-digit number or LC. In Northern Virginia, the ones we see most are 11 (it didn’t light), 12 (the flame went out), 10 (the air or exhaust is blocked) and LC (scale in the heat exchanger, time to descale). Turning the power off and on clears most codes once. If the same code comes back, the code is the answer, and another reset won’t change it.
The codes
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| Code | What it means | What to try first |
|---|---|---|
| 10 | Air supply or exhaust blocked | Look at the vent pipes outside: leaves, a nest, snow, a crushed pipe |
| 11 | No ignition: it tried to light and couldn’t | Is the gas valve to the heater open? Do the other gas appliances work? On propane, check the tank |
| 12 | Flame failure: it lit, then lost the flame | The same checks as 11, plus the vent. Then call |
| 14 | Thermal fuse: something overheated | Call. Don’t keep resetting it |
| 16 | Over temperature | Turn it off and call |
| 25 | Condensate drain blocked | Check the small drain line for a kink or a clog |
| 61 | Combustion fan problem | Call |
| 79 | Water leak inside the unit | Shut off the water and gas to it, and call |
| LC | Scale build-up in the heat exchanger | Book a descale |
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Codes 11 and 12, the most common
Code 11 means the heater asked for gas, sparked, and never saw a flame. On a new install or after any gas work, it’s often air in the line. Otherwise it’s the gas supply: a valve partly closed, a propane tank running low, or a gas line too small for the heater. A tankless at full fire burns up to about five times the gas a tank does, so an undersized line can run the stove fine and still starve the heater. Code 12 means it lit and then lost the flame, which points at the same gas supply, the vent, or a dirty flame rod.
LC means scale
LC, often followed by a number, means scale has built up in the heat exchanger. Northern Virginia’s hard water gets there faster than people expect. You can clear the code, but no button clears the scale: it keeps coming back until the heat exchanger is flushed with a descaling solution. Our tankless descale is $300, regularly $350, booked through the water heater flush page. Here’s what tankless maintenance involves and more on hard water here.
Code 79: water where it shouldn’t be
79 means the leak sensor found water inside the cabinet. Shut the water valve to the heater and the gas valve, turn it off, and call. A small drip inside a tankless is a quick fix early and a much bigger one once it reaches the circuit board.
Power outages and freezing
Rinnai units have small built-in heaters that keep them from freezing, and those run on electricity. In a winter power outage, that protection stops. If the power is going to be out for hours in freezing weather, the heater should be drained.
How old is my Rinnai?
The first two letters of the serial number are the date. The first letter is the year (J for 2017, K for 2018, L for 2019, M for 2020, N for 2021), and the second is the month, A for January. So a serial starting KC was made in March 2018. A tankless that gets descaled often lasts 15 to 20 years, so age matters less here than on a tank. Whether it’s been descaled matters more.
When it’s a repair and when it’s a reset
Reset once. If the code comes back, stop resetting: on 14, 16 and 79, a reset can cover up a real problem. Our tankless problems guide covers the symptoms that don’t throw a code, like water that runs hot, cold, then hot again. A Navien uses different codes; here’s the Navien chart. We repair and descale Rinnai heaters across Northern Virginia; more on our Rinnai page, and how they compare in the best tankless brands.
Book it
A plumbing diagnosis visit is $49, or $250 after hours, and you get the price of the fix before we start. Call (703) 997-9757, day or night, or book the water heater flush from goswiftpro.com/cookiesoffer by November 30 and a box of warm MOLTN cookies comes with it. Every current deal is on our offers page. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
How do I reset a Rinnai tankless water heater?
Turn it off at the controller or cut the power for a minute, then turn it back on. That clears most codes once. If the code returns, the code tells you what to fix.
What does code 11 mean on a Rinnai?
No ignition. It tried to light and never saw a flame. Check that the gas valve is open and the other gas appliances work; on propane, check the tank.
What does LC mean on a Rinnai tankless?
Scale has built up in the heat exchanger. It needs a descale; clearing the code doesn’t remove the scale.
What does code 79 mean on a Rinnai?
The leak sensor found water inside the unit. Shut off the water and gas to it and call.
How often should a Rinnai tankless be descaled?
Every year or two in most Northern Virginia homes, and sooner on hard water or once LC shows up.
