# Tankless Error Codes: Navien, Rinnai, Noritz | Total Tankless > What ignition, flame loss, venting and sensor codes mean across major brands, safe homeowner checks, and when to stop and call a pro. URL: https://socaltotaltankless.com/guide/tankless-water-heater-error-codes/ Last-Modified: 2026-10-10 Tags: tankless water heater error codes ![Tankless controller display showing an error code on a hallway wall](/images/featured/tankless-water-heater-controller-display-showing-a.webp) ## Why Your Tankless Shows an Error Code A tankless unit constantly monitors itself to ensure your endless hot water runs safely. When water flow, gas pressure, or exhaust levels fall outside safe limits, the system shuts down the burner and displays a code. This diagnostic number tells you exactly where to look for the problem. We see these codes as a helpful safety feature rather than a complete malfunction. A returning code means a component needs attention, and our tankless water heater repair [/tankless-water-heater-repair/ →](/tankless-water-heater-repair/) team diagnoses tankless water heater error codes on all major brands across Southern California. ## Code Groups by Brand Tankless error codes typically fall into universal categories like ignition failure or scale buildup. Each brand uses a completely different numbering system for their modern models. We always recommend confirming these numbers against your specific owner’s manual. Meanings often vary between product lines, but most modern units share similar safety triggers. | Code group | What it usually means | Example codes | | --- | --- | --- | | Ignition failure | Burner didn’t light | Rinnai 11, Noritz 11, Navien E003 | | Flame loss | Burner lit, then lost the flame | Rinnai 12, Noritz 12, Navien E012 | | Air supply or exhaust | Blocked vent, fan issue or poor combustion air | Rinnai 10, Noritz 90 (abnormal combustion) | | Overheat | Water or heat exchanger too hot, often from scale or low flow | Rinnai 16 | | Scale warning | Maintenance reminder for scale buildup | Rinnai LC codes | | Sensor faults | Thermistor or flow sensor reading out of range | Varies by brand | ![Technician reading code history on a diagnostic tablet connected to a tankless unit](/images/content/technician-reading-error-code-history-on-a-diagnos.webp) ### Ignition failure codes An ignition failure code means the unit tried to spark the burner but could not establish a fire. The Rinnai error code 11, Noritz 11, and Navien E003 all point to this specific problem. We frequently trace this back to a closed gas valve, an undersized gas line, or a dirty flame rod. Residential natural gas units generally need a minimum of 3.5 inches of water column pressure to ignite properly. Our guide on why a tankless won’t ignite [/guide/tankless-water-heater-not-igniting/ →](/guide/tankless-water-heater-not-igniting/) goes deeper into these gas pressure issues. Seismic shutoff valves in Southern California homes can sometimes partially trip and restrict this vital gas flow. ### Flame loss codes Flame loss occurs when the burner lights successfully but the sensor suddenly stops detecting the fire. The Rinnai 12, Noritz 12, and Navien E012 codes indicate this exact sequence. We often fix this by cleaning the flame rod, which gets coated in a white silica or carbon buildup over time. If the code appears when running multiple showers, the home’s gas meter might be undersized for the demand. ### Venting and combustion codes Venting codes appear when the internal fan detects poor airflow or blocked exhaust pathways. The Rinnai 10 and Noritz 90 codes specifically warn of abnormal combustion air drops. Our technicians frequently find lint blocking the intake screen when the unit sits near a laundry dryer. Treating these warnings seriously prevents dangerous carbon monoxide from backing up into the surrounding space. A failing internal fan or a disconnected PVC exhaust pipe will also trigger an immediate system halt. ### Overheat and scale codes Overheat codes trigger when scale inside the heat exchanger traps heat and dangerously restricts water flow. The Rinnai 16 code specifically signals that the internal temperatures have exceeded safe operating limits. We highly recommend installing a pre-filter or water softener to protect your eco-friendly investment. Los Angeles water averages around 12.7 grains per gallon of hardness, causing scale to build up rapidly without filtration. Rinnai’s “LC” maintenance code flashes around 3,000 hours of operation as a built-in reminder to flush the system. ### Sensor codes Sensor errors mean the control board receives incorrect data from the internal temperature or water flow monitors. The unit will refuse to run if these thermistors read out of range. Our team can usually resolve this by replacing the faulty thermistor, which is an affordable repair involving a $20 to $40 part. Flow sensors use a tiny magnetic turbine to detect water movement. A small piece of hard water debris can easily jam this turbine and stop your hot water entirely. ## Safe Homeowner Checks You can perform a few basic safety checks before scheduling a professional service visit. Addressing simple power or water supply issues often clears the code without any outside help. We suggest walking through these steps only if you feel completely comfortable doing so. Check the list below for safe troubleshooting methods. 1. **Gas supply.** Is the gas shutoff valve to the unit fully open? If your kitchen stove refuses to light, the issue likely stems from the main city gas supply to the house. 2. **Power.** Gas tankless systems require a standard 120-volt electrical connection to operate the computer board. Check that the unit is plugged in and the GFCI outlet has not tripped. 3. **One reset.** Turn the unit off and on once using the reset procedure outlined in your manual. 4. **Inlet filter screen.** Many modern units have a small stainless steel mesh screen where the cold water enters. A quick cleaning with an old toothbrush and white vinegar can resolve low-flow problems. 5. **Vent terminations.** Inspect the exterior walls or roof for leaves, bird nests, or debris blocking the intake and exhaust pipes. ![Inlet water filter screen removed from a tankless unit with light scale visible](/images/content/inlet-water-filter-screen-removed-from-a-tankless-.webp) > **Gas safety comes first** > > If you smell gas, don’t touch switches or the unit. Leave the house and call your gas company or 911 from outside. Never open the unit’s sealed combustion chamber or adjust gas components yourself. ## When to Stop and Call Stop troubleshooting and book a professional diagnosis if you feel unsafe or if the unit shows specific warning signs. A persistent issue requires specialized testing equipment to pinpoint the exact failure. We always advise homeowners to prioritize their personal safety around natural gas appliances. Call an expert immediately if you notice any of the following conditions. - The same code returns after one complete reset cycle - You see any venting, exhaust, or combustion code on the digital display - You smell a rotten egg gas odor or exhaust fumes near the unit - There is water actively leaking from the bottom of the casing - The system starts making loud, vibrating noises during operation - The code appeared immediately following recent plumbing or venting work ## Why Repeated Codes Point to Deeper Faults A code that clears with a reset and comes back days later serves as a symptom rather than the root problem. Simple resets cannot fix low incoming gas pressure, thick calcium scale, or a failing internal sensor. Our service process starts by reading the unit’s stored code history to identify long-term fault patterns. Technicians use digital manometers to test the gas pressure statically and under a full heavy load. Repeated ignition attempts over several weeks place heavy stress on expensive electrical components. We then inspect and clean the flame rod, test the electrical resistance of the thermistors, and confirm the PVC vent is completely sealed. You receive full written findings and a precise repair quote before any wrench touches the system. ## Common Root Causes We Find Identifying the true root cause often requires matching the specific error code to the physical symptoms of the system. Our field data shows that incorrect gas line sizing causes a significant portion of new installation failures. The chart below outlines the most frequent component failures and their standard professional solutions. | Root cause | Codes it often triggers | Typical fix | | --- | --- | --- | | Undersized gas line | Ignition failure, flame loss | Upsize the supply line directly from the meter | | Dirty flame rod | Flame loss | Clean or replace the rod assembly | | Scale in heat exchanger | Overheat, scale warning, low flow | Descale with a professional vinegar flush | | Blocked vent | Air supply or exhaust | Clear obstructions and reseal the PVC vent | | Failed sensor | Sensor faults | Swap out the broken thermistor or flow sensor | Regular professional maintenance effectively prevents the majority of these expensive breakdowns. See what happens during tankless maintenance [/guide/what-happens-during-tankless-maintenance/ →](/guide/what-happens-during-tankless-maintenance/) to learn how an annual tune-up protects your system. If your unit is showing a code right now, send us the brand, the code, and a photo through our contact form [/contact/ →](/contact/) . Our service dispatchers will quickly review the details and explain the most likely repair strategy. FAQ\_LOG ## Common Questions ### Is it safe to reset my tankless water heater after an error code? One reset is fine. If the same code comes back, there's an underlying fault, such as low gas pressure, a dirty flame rod or a blocked vent. Stop resetting and schedule a diagnosis. Never keep resetting a unit that shows a venting or exhaust code. ### Do error codes mean the same thing across brands? No. Each manufacturer uses its own numbering. A code 11 on one brand may not match a code 11 on another, even when the faults are similar. Always check your model's manual or the label inside the front cover. ### Can you fix tankless error codes that other plumbers couldn't? Complex error-code diagnosis is one of our core specialties. We read the unit's code history and test the parts behind the code rather than just clearing it, which is why many of our repair calls come from homeowners who already had someone out. FROM GUIDE TO SERVICE Learn more about Tankless Water Heater Repair Diagnostic troubleshooting and repair for error codes, faulty flow sensors, ignition failures and valve replacements. Factory-certified technicians, published pricing and a free virtual estimate before we visit. View Repair [/tankless-water-heater-repair/ →](/tankless-water-heater-repair/) Free Estimate [/contact/ →](/contact/) TECH\_LIBRARY ## More Repair Guides Keep reading: related answers from the same topic cluster. GUIDE\_01 · concern ### Warning Signs Your Tankless Water Heater Needs Repair Fluctuating temperature, reduced flow, units not firing at low flow, odd noises or exhaust smell, and how urgent each sign is. Read Guide [Warning Signs Your Tankless Water Heater Needs Repair →](/guide/signs-tankless-water-heater-needs-repair/) GUIDE\_02 · cost ### How Much Does Tankless Water Heater Repair Cost in California? How tankless repair pricing works: diagnostic fee structure, common repairs by part, warranty parts vs labor, and no hidden admin fees. Read Guide [How Much Does Tankless Water Heater Repair Cost in California? →](/guide/tankless-repair-cost-california/) GUIDE\_03 · comparison ### Tankless Water Heater Repair vs. Replacement: How to Decide Weigh unit age, warranty status, heat exchanger condition and repair cost vs a new install ($4,500–$7,500) to make the right call. Read Guide [Tankless Water Heater Repair vs. Replacement: How to Decide →](/guide/tankless-repair-vs-replacement/) GUIDE\_04 · scenario ### Why Does My Tankless Water Heater Go Cold Mid-Shower? Cold water sandwich, minimum flow activation, check-valve issues, undersizing and scale: what's normal and what needs repair. Read Guide [Why Does My Tankless Water Heater Go Cold Mid-Shower? →](/guide/tankless-water-heater-goes-cold-in-shower/) GUIDE\_05 · scenario ### Tankless Water Heater Leaking: Causes and What to Do First Shutoff steps, common leak sources (fittings, relief valve, condensate line, heat exchanger) and when a leak means replacement. Read Guide [Tankless Water Heater Leaking: Causes and What to Do First →](/guide/tankless-water-heater-leaking/) GUIDE\_06 · scenario ### Tankless Water Heater Won't Ignite: Causes of Ignition Failure Gas supply and pressure, dirty flame rods, igniters, vent blockage, and flame-loss vs ignition-failure codes, plus a gas safety warning. Read Guide [Tankless Water Heater Won't Ignite: Causes of Ignition Failure →](/guide/tankless-water-heater-not-igniting/)