# Tankless Water Heater Error Codes Explained: Rinnai, Navien, Noritz, and Rheem (What to Try Before You Call)

*Published 2026-10-08 by Hugo Plumbing, Houston, TX.*

What the common Rinnai, Navien, Noritz, and Rheem tankless error codes mean, the safe resets a Houston homeowner can try, and which codes mean call a plumber.

A tankless water heater does not fail quietly. When something is wrong it shuts down, shows a two- or three-character code on the display, and waits. That code is the unit telling you exactly what it checked and what failed, and most of the time the fix is something simple you can confirm in five minutes: gas is off, the vent outside is blocked, the condensate line is full, or the heat exchanger is scaled up from Houston water. This guide decodes the common codes on the four brands most Houston homes have (Rinnai, Navien, Noritz, and Rheem), tells you what is safe to try, and names the codes that mean stop and call. If you would rather have a licensed master plumber read it, the diagnosis visit is free, 24/7, at (713) 409-7176.

## Error Codes by Symptom Family

Every brand numbers its codes differently, but they all describe the same handful of failures. Find your code in the table, then read the matching section below.

| Problem family | Rinnai | Navien | Noritz | Rheem / Richmond |
|---|---|---|---|---|
| Ignition failure (never lights) | 11 | E003 | 11 | 11 |
| Flame loss or weak flame while running | 12 | E012 | 12 | 12 |
| Overheat, thermal fuse, or scale | 14, 16, LC | E016 | 14, 16 | LC |
| Venting, air supply, or combustion fan | 10, 61 | E030, E110 | 90 | 13 |
| Condensate drain blocked (condensing models) | 25, 29 | | 29 | 29 |
| Sensor, electrical, or leak detected | 19, 32, 79 | | | 76 |

Rheem code 29 can mean either the heat exchanger outlet temperature is too low or the condensate neutralizer is blocked, which is why it sits in the condensate row. Rheem 76 is a communication fault with the remote controller, not a heating problem.

## Ignition Failure: Rinnai 11, Navien E003, Noritz 11, Rheem 11

The unit tried to light the burner and never saw a flame. Gas supply is the usual reason.

1. **Confirm gas is on.** Check that the gas shutoff valve on the supply pipe has its lever in line with the pipe. Then test another gas appliance, a stove burner or the furnace. If nothing in the house lights, the problem is the meter or the gas company, not the heater.
2. **Check the vent termination outside.** A wasp nest, leaves, or a bird in the intake starves the burner of air and the controller reports it as an ignition failure. Clear anything you can reach without a ladder.
3. **Power-cycle the unit.** Switch it off at the power switch, unplug it, or flip the breaker. Wait 30 seconds, restore power, open a hot tap.
4. **If it lights and stays lit, watch it for a day.** If code 11 or E003 returns, the igniter, flame rod, or gas valve is failing and needs a plumber with a manometer to check gas pressure at the unit.

**If you smell gas at any point, stop.** Leave the house and call the gas company from outside. Our guide on [what to do if you smell gas](/blog/smell-gas-in-house-what-to-do) covers the next steps.

## Flame Loss While Running: Rinnai 12, Navien E012, Noritz 12, Rheem 12

The burner lit, then the flame went out or weakened partway through a shower. Three things cause this in Houston homes:

- **Wind at the vent.** Terminations that face an open fence line or a corner where wind wraps around the house get gusts pushed back into the exhaust. The flame flutters, the sensor loses it, and the unit shuts down. This is the code that shows up only on windy days.
- **Low gas pressure.** A gas line that was sized for a tank heater and never upgraded for the tankless conversion starves the burner at full fire. The code appears when the unit is working hardest: two showers plus the dishwasher. Our [tankless installation](/services/tankless-water-heater-installation) page explains why gas sizing is part of a correct install.
- **A dirty flame rod.** After years of service the sensor that confirms the flame gets a film of oxide and reads the flame as weaker than it is. Cleaning it is a plumber job because the burner assembly has to come apart.

Power-cycle once. If the code comes back on calm days with no other gas appliance running, book a visit.

## Overheat and Scale: Rinnai 14, 16, LC; Navien E016; Noritz 14, 16; Rheem LC

This is the family Houston homes see most. Hard water leaves calcium carbonate inside the heat exchanger, the passages narrow, water moves slower across the same flame, and the outlet temperature spikes. The unit either warns (Rinnai 16, Rinnai LC, Rheem LC) or trips the thermal fuse and shuts down (Rinnai 14, Noritz 14, Navien E016).

The LC code is unusual because the heater keeps running. The display alternates LC with the set temperature, and some homeowners live with it for a year. Do not. It is the last warning before a thermal fuse trip, and a thermal fuse is a part replacement, not a reset.

1. **Check for restricted flow first.** Make sure the cold inlet valve is fully open and that the inline filter screen (a small cap on the cold side of most units) is not packed with sediment. A half-closed valve mimics scale.
2. **Flush the heat exchanger.** This is the fix. A descaling flush pumps a vinegar or citric solution through the exchanger for 45 to 60 minutes using the isolation valves below the unit. Our guide on [how often to flush a tankless in Houston](/blog/tankless-water-heater-flush-how-often-houston) explains the interval and why it is shorter here.
3. **If there are no isolation valves,** you cannot flush it without cutting pipe. Ask to have an isolation valve kit added; it turns a two-hour job into a 45-minute one every year after.
4. **After a thermal fuse trip (14),** the fuse has to be replaced before the unit will run again. That is a plumber visit, and the flush should happen at the same time or the new fuse will trip too.

Scale is also the reason a tankless that should last 20 years quits at 12. Our guide on [how long a tankless lasts in Houston](/blog/how-long-does-a-tankless-water-heater-last-houston) covers what maintenance buys you.

## Venting and Air: Rinnai 10, 61; Navien E030, E110; Noritz 90; Rheem 13

The controller measures airflow through the combustion fan and the pressure at the intake and exhaust. When those read wrong, you get a venting code.

- **Check the outside termination.** Nests, leaves, a dryer vent blowing lint into the intake, or a fence or shrub built too close since the install. Clear what you can see.
- **Check for ice during a freeze.** Condensing units exhaust cool, wet gas that can freeze at the termination on the coldest nights.
- **Listen for the fan.** If you hear nothing when a tap opens, the combustion fan (Rinnai 61) may have failed. That is a part.
- **Attic and exterior units in summer.** A unit in a 140°F attic or in full west sun on an exterior wall works harder to move air. Make sure nothing has been stored against the intake.

If the vent run is long or has too many elbows (common when a tankless replaced a tank heater in the same closet), the unit will throw venting codes under load forever until the vent is corrected.

## Condensate: Rinnai 25, 29; Noritz 29; Rheem 29

Condensing tankless units (the high-efficiency ones with PVC venting) produce a small stream of acidic water that drains through a neutralizer cartridge and a drain line. When that line clogs or the trap fills with debris, the unit stops to protect itself.

1. Find the clear or black drain tube leaving the bottom of the unit.
2. Check that it runs downhill the whole way to a drain and is not kinked or pinched.
3. If a neutralizer cartridge is in the line, it may be packed solid; the media needs replacing every one to two years.
4. Clear the line, power-cycle, and run a tap.

## Sensors, Electrical, and Leaks: Rinnai 19, 32, 79; Rheem 76

- **Rinnai 19** is an electrical grounding fault. Do not keep resetting it. Have a plumber or electrician check the outlet and the unit's ground.
- **Rinnai 32** is the outgoing water temperature sensor. A reset may clear it once; a repeat means the sensor is failing.
- **Rinnai 79** is a water leak detected inside the cabinet. Shut off the cold inlet valve and the power and call. Our guide on [how to shut off a water heater](/blog/how-to-turn-off-your-water-heater-houston) covers the tankless isolation valves.
- **Rheem 76** is a communication fault between the unit and its remote. Check the thin control wire and its connections at both ends; it is often a loose plug, not a failure.

## What Is Safe to Try, and What Is Not

| Safe for a homeowner | Leave to a plumber |
|---|---|
| Confirm the gas valve is open and other gas appliances work | Anything after a gas smell |
| Clear the outside vent termination and intake screen you can reach from the ground | Opening the burner or fan assembly |
| Check and clear the condensate drain line and replace neutralizer media | Replacing a thermal fuse, flame rod, igniter, or sensor |
| Clean the inline cold-water filter screen | Gas pressure testing with a manometer |
| Power-cycle once and run a hot tap to clear air | Any code that returns after one power cycle |
| Check the remote controller wire connections | Leak code 79, electrical code 19, repeated ignition codes |

## When to Call

Call Hugo Plumbing when:

- You smell gas. Leave first and call the gas company from outside, then call us for the repair.
- Any ignition, flame, or venting code returns after a single power cycle.
- You see Rinnai 79 (leak inside the unit) or 19 (grounding fault).
- The LC or overheat code is on and the unit has not been flushed in over a year, or it has no isolation valves.
- A thermal fuse has tripped (Rinnai 14, Noritz 14, Navien E016 that will not clear).
- The unit shows no code but delivers lukewarm water or cycles hot and cold; that is often a flow or crossover problem covered in our guide on [why hot water takes so long](/blog/hot-water-takes-too-long-houston), or a gas supply that is too small.

If the display is blank and nothing happens when you open a tap, start with our [no hot water troubleshooting guide](/blog/no-hot-water-troubleshooting-houston) before assuming the heater is dead.

The diagnosis visit is free, with no trip charge or diagnostic fee, and you get a flat written price before any work starts. Tankless repairs and annual flushes through our [water heater maintenance](/services/water-heater-maintenance) service are priced on site because the brand, access, and what the code turns out to mean change the job. Licensed master plumbers (MPL 41319) are on call 24/7 at (713) 409-7176.

## Frequently Asked Questions

**What is the most common tankless water heater error code in Houston?**

The overheat and scale family: Rinnai 14 and LC, Navien E016, Noritz 16, and Rheem LC. Houston water is hard, and the minerals it leaves inside the heat exchanger narrow the passages until the unit either overheats or reports scale outright. An annual descaling flush through the isolation valves prevents most of these codes.

**Can I reset a tankless water heater error code myself?**

Yes, for most codes. Turn the unit off at its power switch or unplug it, wait 30 seconds, restore power, and open a hot tap. If the code clears and stays clear, it was a one-time event such as a gust at the vent or air in the line. If it comes back within a day or two, something physical is wrong and a reset will keep clearing it until the part fails completely.

**What does the LC code on a Rinnai mean, and is it urgent?**

LC (shown as LC0 through LC9) means scale has built up in the heat exchanger. The unit keeps running and alternates LC with the set temperature. It is not an emergency, but it is the only warning you get before the exchanger overheats, so schedule a descaling flush soon. Running it for months with LC on the display shortens the life of the heat exchanger.

**Why does my tankless heater throw an ignition code only when it is windy or cold?**

Ignition and flame-loss codes (Rinnai 11 and 12, Navien E003 and E012, Noritz 11 and 12, Rheem 11 and 12) often trace back to the vent. Wind pushing into a termination that faces an open fence line, a bird nest in the intake, or ice on the exhaust during a freeze all disturb the flame. Check the outside termination first, then the gas supply.

**When should I stop troubleshooting and call a plumber?**

Stop immediately if you smell gas; leave the house and call the gas company from outside. Call a plumber for any leak code such as Rinnai 79, for ignition or flame codes that return after one power cycle, for electrical codes like Rinnai 19, and for any code that keeps clearing and coming back. Hugo Plumbing comes out free, 24/7, and gives you a flat written price before touching the unit.

If your tankless won't stop flashing codes, call Hugo.

## Frequently Asked Questions

### What is the most common tankless water heater error code in Houston?

The overheat and scale family: Rinnai 14 and LC, Navien E016, Noritz 16, and Rheem LC. Houston water is hard, and the minerals it leaves inside the heat exchanger narrow the passages until the unit either overheats or reports scale outright. An annual descaling flush through the isolation valves prevents most of these codes.

### Can I reset a tankless water heater error code myself?

Yes, for most codes. Turn the unit off at its power switch or unplug it, wait 30 seconds, restore power, and open a hot tap. If the code clears and stays clear, it was a one-time event such as a gust at the vent or air in the line. If it comes back within a day or two, something physical is wrong and a reset will keep clearing it until the part fails completely.

### What does the LC code on a Rinnai mean, and is it urgent?

LC (shown as LC0 through LC9) means scale has built up in the heat exchanger. The unit keeps running and alternates LC with the set temperature. It is not an emergency, but it is the only warning you get before the exchanger overheats, so schedule a descaling flush soon. Running it for months with LC on the display shortens the life of the heat exchanger.

### Why does my tankless heater throw an ignition code only when it is windy or cold?

Ignition and flame-loss codes (Rinnai 11 and 12, Navien E003 and E012, Noritz 11 and 12, Rheem 11 and 12) often trace back to the vent. Wind pushing into a termination that faces an open fence line, a bird nest in the intake, or ice on the exhaust during a freeze all disturb the flame. Check the outside termination first, then the gas supply.

### When should I stop troubleshooting and call a plumber?

Stop immediately if you smell gas; leave the house and call the gas company from outside. Call a plumber for any leak code such as Rinnai 79, for ignition or flame codes that return after one power cycle, for electrical codes like Rinnai 19, and for any code that keeps clearing and coming back. Hugo Plumbing comes out free, 24/7, and gives you a flat written price before touching the unit.

## About the Author

Hugo Plumbing is a licensed, insured, family-run plumbing company in Houston, Texas providing residential and commercial plumbing repair, replacement, and installation, with 24/7 emergency service. Services: https://hugoplumbingtx.com/services · Book: https://book.housecallpro.com/book/Hugo-Plumbing/a36279ec67c14456b0b25f1f992b2f4e?v2=true · Call: (713) 409-7176

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