Tankless units have earned their spot in Charlotte homes for good reason. They sip gas compared to older tanks, deliver endless hot water when they are tuned right, and take up a fraction of the space. The flip side shows up on the display when the shower turns cold and the heater throws an Error 11 or Error 12. If you have a Rinnai, Noritz, Navien, Takagi, or Rheem tankless model, you have likely seen one of these at least once. They both point to ignition and combustion issues, but they have different root causes and different ways to diagnose them.
What follows comes from years crawling through crawlspaces in Myers Park, swapping valves in split-levels in Matthews, and flushing heat exchangers in Ballantyne attics in July heat. You will find practical steps you can try safely, what to leave to a pro, and the judgment calls around repair, water heater replacement, and, when it makes sense, water heater installation for an upgrade. I will keep the jargon light and explain what matters: the fuel, the air, the water, and the control logic that ties them together.
What Error 11 and Error 12 actually mean
Manufacturers use slightly different phrasings, but across brands the meaning is consistent.
Error 11 usually means the unit commanded ignition and did not verify a flame. Think of it as failed ignition. The control board opened the gas valve and sparked, but the flame sensor did not see fire. You will get a short attempt, a click, possibly a whoosh that doesn’t hold, then the unit locks out.
Error 12 indicates flame loss during operation. The unit did light, ran for a bit, then the flame went unstable and dropped out. You will notice hot water for a few seconds or minutes, then a sudden chill as the burner quits and the code appears.
Both codes sit at the intersection of three basics: sufficient gas volume and pressure, clean combustion air and proper venting, and a clean, properly flowing water path. A fourth piece rides above them: the control system that reads sensors, sparks, and protects you by shutting things down when it sees something off.
How Charlotte homes set the stage
Local context matters. Charlotte homeowners deal with a few patterns I see again and again.
Natural gas pressure from Piedmont Natural Gas in most neighborhoods holds steady in the 7 to 10 inches water column range at the meter, which is fine for residential appliances. The trouble shows up inside the house. Long runs of undersized half-inch black iron or CSST feed kitchens, dryers, furnaces, and then a tankless unit that wants a lot more fuel than the old 40-gallon tank ever needed. When a furnace and the water heater fire together on a cold January morning, gas pressure at the water heater drops and up pops Error 11 or 12.
Air quality inside tight crawlspaces and small closets can also fool a water heater. Vent lengths on existing installs sometimes push the limits, or the termination is tucked under an eave where wind swirls back into the intake. That creates a backdraft that a flame sensor reads as instability, again triggering Error 12.
Charlotte water runs moderately hard. Scale builds up inside heat exchangers in two to five years if the unit lacks treatment. A partially blocked exchanger restricts water flow and shifts temperature control out of its happy range. The burner scales down, then up, hunting for stability. That hunting can misfire, leading to error codes during long showers or filling a tub.
Finally, pollen season. It sounds trivial, but I have pulled bright yellow filters from outdoor Noritz units each spring. A clogged intake screen starves combustion air. It shows up as both 11 and 12 depending on how choked things get.
First checks you can do without tools
Before calling a technician, there are a few safe checks. Do not open gas lines or remove sealed combustion covers unless you are qualified. Most modern tankless units consider the front panel a sealed part of the venting system. Removing it can introduce carbon monoxide risk if the unit runs.
- Confirm basic demand. Open a hot tap at a sink and let it run for two minutes. Some units need a minimum flow rate, often around 0.5 to 0.7 gallons per minute, to start and stay lit. Tiny trickles during a hand wash may fail to ignite. Try a shower or tub filler. If the code happens only on low-flow fixtures, a flow sensor or aerator clog may be part of the story. Inspect the intake and exhaust terminations. For outdoor units, look for leaves, spider webs, pollen matting, or a bird nest. For indoor direct-vent units, make sure the exterior vents are clear, not blocked by mulch, ivy, or a snow drift in rare storms. During high winds, wind tunnel effects under soffits can disrupt combustion. If your vent ends under an eave, note that detail for your technician. Power cycle the unit properly. Shut off power at the switch or breaker for 30 seconds, then restore. Some control boards need a full reset to clear lockout. If the code returns immediately, there is an active fault rather than a one-time glitch. Check the condensate drain on condensing units. If you see a clear vinyl hose leaving the bottom of the unit, make sure it is not kinked or clogged. When the trap backs up, water can drip into the combustion chamber, destabilize the flame, and throw Error 12. Fixing the trap often clears recurring codes. Listen and smell. When the unit tries to fire, do you hear repeated clicking without a whoosh? That fits Error 11. Do you hear a whoosh, hot water starts, then the burner shuts down after 10 to 60 seconds? That fits Error 12. Do you smell gas at the unit during an ignition attempt? If so, stop and call a pro. Do not keep cycling it.
If any of those checks reveal blockage or a simple reset helps, you may be back in business. If not, time to look deeper.
Gas supply: sizing, pressure, and regulators
A tankless burner is hungry. A 180,000 BTU unit wants more fuel at peak than a furnace in many Charlotte homes. The old tank likely used around 40,000 BTU. When a tankless replaced it without upsizing gas lines, ignition can be unreliable.
I carry a manometer on every call. Numbers cut through guesswork. At the appliance gas valve, static pressure should be within the manufacturer’s band, commonly 7 to 10 inches water column for natural gas and 11 to 13 for propane. The key test is dynamic pressure. With the water heater firing, pressure should not sag more than about 1 to 2 inches WC under load. If it drops to 4 or 5 inches on natural gas, the flame will stumble. That produces Error 12, and if the sag occurs right at light-off it can be Error 11.
Aged regulators at the meter sometimes drift low. More often, the branch to the water heater runs 40 to 60 feet through half-inch pipe with multiple elbows and tees that serve other appliances. Flow capacity isn’t just the nominal pipe size. Fittings, length, and shared demand matter. The fix might be as straightforward as a dedicated three-quarter-inch run to water heater repair charlotte the water heater, or as surgical as relocating tees to reduce pressure drop when the furnace lights.
For propane homes in the outskirts of Mecklenburg, watch the second-stage regulator near the house. If it frosts heavily during heavy draw or the tank is nearly empty, pressure collapses at the wrong moment. Keeping propane above a quarter tank and replacing tired regulators prevents a lot of mystery codes in winter.
Combustion air and venting details that trip people up
Direct-vent tankless units draw combustion air from outside and send exhaust outside through concentric or twin-pipe systems. The rules are simple on paper and fussy in practice. Exceeding the maximum equivalent length by a few elbows can leave the burner starved for air. Combining intake and exhaust terminations too close to each other lets exhaust recirculate into the intake. Wind can create pressure pulses at the vent that show up as flame loss.
I see three recurring problems around Charlotte:
- Intake screens clogged by pollen or construction dust after a renovation. Clean the screens gently with a soft brush and vacuum. Shared vent chase with a high-efficiency furnace. If both appliances pull air from the same confined space, negative pressure can upset one or both. Separation or additional makeup air solves it. Terminations under decks or near corners. Wind can swirl under a deck and bounce exhaust right back. Moving the termination a few feet or adding wind baffles fixes stubborn Error 12 complaints.
Outdoor units present their own challenge. Spiders love the warmth. Webbing and dead insects can block the burner screen. Manufacturers offer burner maintenance kits for this reason, and a seasonal cleaning keeps the flame stable.
Water-side issues: scale, filters, and flow sensors
Tankless heaters depend on steady flow through tiny passages in a heat exchanger. Scale narrows those passages. With Charlotte’s water at around 5 to 8 grains of hardness in many neighborhoods, unprotected tankless units often need descaling every 12 to 24 months. Homes on wells tend to scale faster and also bring sediment into the mix.
Inside the heater, a flow sensor measures the water moving through the unit to tell the control board when to fire and how hard. If the sensor sticks or reads low because of scale or debris, the board may starve the burner, leading to repeated light-off attempts and Error 11. If scale restricts flow, the unit may short-cycle the flame to avoid overheating a small water volume, which can drop the flame and flash Error 12.
Flushing with a pump, hoses, and white vinegar or a citric acid solution for 45 to 60 minutes dissolves scale. I prefer citric acid for its lower odor and predictable strength. While flushing, I pull and clean inlet screens at the cold and hot service valves. You would be surprised how much PVC shavings and sand sit there after a remodel or new water heater installation Charlotte homeowners did a year before.
If you have a recirculation loop, make sure the check valve functions and the loop is balanced. A misbehaving recirc can send hot water back into the cold inlet and confuse the temperature logic, which then chases the setpoint and sometimes drops flame.
Electrical and control basics
Ignition demands spark strength and clean signals from sensors. Low voltage at the outlet after a power strip, weak ground, or a shared circuit with a treadmill or freezer can introduce electrical noise or starve the igniter. Most tankless units need a solid 120 volts. I see outlets in attic installations where voltage sags to 108 under load with a long run and loose connections. Tighten terminations, correct the circuit, and the misfires disappear.
Flame sensors, which are often simple metal rods in the flame path, build light oxidation. A gentle cleaning with very fine abrasive cloth restores signal. Igniters wear over time. At six to ten years old, many units benefit from a new igniter and flame rod as part of a tune-up. Control boards fail less often, but when all else checks out and signals show up erratically, a board may be the culprit.
On some models, a dirty or misaligned air-fuel ratio (AFR) sensor will cause nuisance Error 12. If your model has an AFR calibration mode, and the gas pressure and venting are correct, a qualified tech can recalibrate it.
How a pro isolates the cause, step by step
A clean diagnosis saves money and time. My flow on a service call for Error 11 or 12 looks like this:
- Listen to the ignition sequence and verify the exact behavior. Note timing with a stopwatch. First failure at light-off versus loss after 10 to 30 seconds heads me in different directions. Check dynamic gas pressure at the valve port during ignition and steady burn with a digital manometer. If pressure collapses, I find where and why. If pressure holds, I move on. Inspect intake and exhaust visually and with a mirror or camera. Measure equivalent vent length. Correct any glaring venting issues before chasing controls. Measure voltage, ground, and neutral integrity at the outlet and inside the unit. Verify the igniter gets proper power. Clean or replace the flame rod if readings look weak. Check the condensate trap for blockages and proper slope to the drain. Clear if needed. Open the service valves and perform a descaling if the unit shows signs of restriction, uneven temperature, or if maintenance history is unknown and the unit is three or more years old. Verify flow sensor operation through diagnostic mode if available. Replace a sticky sensor.
By the end of that path, I can tell a homeowner whether the issue was a simple maintenance gap, a gas supply limitation, a venting correction, or a failing part. The parts bill on many of these calls runs modest: gaskets, sensors, and igniters are typically in the double to low triple digits, plus labor. Gas line or venting corrections vary widely based on access.
When repair makes sense, and when replacement is smarter
Age and condition drive the choice. For a unit under 8 years old with otherwise clean internals and good installation bones, tankless water heater repair almost always pencils out. Swapping an igniter, flame rod, or flow sensor can buy years of service. If your problem stems from plumbing or vent layout, fix the infrastructure rather than the appliance.
Between 10 and 15 years, look harder at the big picture. If a heat exchanger leaks or shows heavy corrosion, if the unit has needed multiple control components in the last 12 months, or if parts are getting scarce, water heater replacement deserves a serious look. Modern units often bring better cold-weather performance, quieter operation, and smarter controls. If your family has grown and you regularly push the capacity, a properly sized upgrade reduces stress on the system and those cold-shower surprises.
When planning water heater installation in Charlotte, account for gas line sizing from the start. Budget for a dedicated line if the existing branch is marginal. Consider a whole-home water treatment approach if hardness or well minerals are part of your reality. Venting should respect manufacturer limits and local code clearances to windows, corners, and property lines. Aligning these details at installation prevents the cascade of intermittent Error 11 and 12 calls later.
Safety notes you should not ignore
Any time you suspect a gas leak, stop. If you smell gas near the unit while it tries to light, shut the gas valve off and call for service. If your carbon monoxide alarm trips during water heater operation, do not reset and forget. Venting faults can backfeed exhaust into living spaces, especially with attic or closet installs. Many attic installs in older Charlotte homes lack secondary containment for condensate. If you see water stains around the unit, address that trap and drain before it soaks insulation and drywall.
Do not bypass safety interlocks. Some online videos suggest jumping sensors to “test” a theory. You do not want to defeat flame failure detection, even for a second. The safety systems exist for a reason.
Preventive habits that keep 11 and 12 away
Think in seasons. I like to pair maintenance with something you already do. Change HVAC filters? That is a good month to service the water heater.
- Flush the heat exchanger annually if you have no softener and your usage runs high, every two years if softened or light use. Keep a log with the date and any findings. Clean intake screens and check vent terminations each spring and fall. Clear spider webs and pollen. Test the condensate drain by pouring a cup of water into the trap and watching it flow. Clear any slime buildup with a mild cleaner. If you are on propane, check regulator health and keep tank levels above a quarter. Once a year, have a licensed pro record gas dynamic pressure at the unit under full burn and verify electrical integrity. These numbers serve as a baseline for troubleshooting later.
These simple steps cost less than a service call and prevent the common, avoidable triggers of Error 11 and 12.
Real examples from Charlotte jobs
A ranch in Cotswold had a three-year-old condensing tankless that threw Error 12 any time two showers ran. Gas pressure at the appliance dropped from 8 inches to 5.2 inches WC when the furnace cycled. The installer had teed off a half-inch branch that also fed the range. We ran a new three-quarter-inch CSST directly from the meter with an upsized meter outlet fitting approved by the utility. Error gone. Total fuel consumption did not change much, but the heater finally got what it needed at the moment it mattered.
In Steele Creek, an outdoor unit flashed Error 11 sporadically. No gas issues, great spark, brand-new igniter. The intake screen looked clean at a glance. When we removed it, the backside was matted with yellow pollen and tiny insects. Cleaned the screen, vacuumed the burner face, and the issue vanished. We added a quick lesson for the homeowner to check the screen each April.
Up in Huntersville, a five-year-old unit would run hot for a minute, then cut out with Error 12, then relight and repeat. The condensate trap had a slug of slime blocking outflow. Condensate backed into the combustion chamber at random, destabilizing the flame. We cleared the trap, routed the drain with a better slope, and added a maintenance reminder. No parts needed.
Cost expectations in the Charlotte market
Prices vary by brand and access, but ballpark numbers help planning. A diagnostic visit with manometer and electrical checks typically runs in the low to mid hundreds. Descaling with service valves already in place runs in a similar band, more if valves need to be added. Flame rod or igniter replacement usually lands under a few hundred including parts and labor. Gas line upsizing across a crawlspace might range from several hundred to over a thousand depending on length and obstacles. Full water heater replacement with a comparable tankless model, venting, and proper gas sizing tends to start in the low thousands and climb with complexity or recirculation features.
Charlotte’s permitting and inspection process is straightforward for water heater replacement and water heater installation. Plan for an inspection window, and make sure your contractor pulls permits when required. It protects you on resale and ensures an extra set of eyes on gas and venting.
Picking a service partner
Tankless systems reward technicians who bring the right tools and patience. Ask a prospective company a few pointed questions. Do they carry a manometer and record dynamic gas pressure? Will they descale and check flow sensors as part of routine service? Are they familiar with your brand’s specific error codes? Do they stock common parts like igniters and flame rods on the truck? Straight answers here separate true tankless water heater repair pros from generalists.
Look for companies that have put in the miles on Charlotte homes specifically. Crawlspace work, venting around eaves, and our pollen-heavy springs create patterns that a local tech will spot in minutes.
When an upgrade aligns with broader plans
Sometimes the water heater is the first domino in a larger home project. If you are remodeling a primary bath, adding a basement suite, or finishing a bonus room over the garage, reevaluating hot water capacity makes sense before drywall closes. A larger unit or a tandem setup, along with a dedicated gas line and improved vent routing, eliminates the borderline scenarios that trigger Error 11 and 12 during peak demand.
If you are converting from electric tank to gas tankless, line sizing is not optional. Plan the gas route early. If you rely on well water, include filtration or softening in the same scope so your new heat exchanger does not scale up in its first year. A smart, integrated water heater installation Charlotte homeowners can live with for 15 years beats a piecemeal approach that leads to callbacks.
A practical mindset for long service life
The best way to think about tankless systems mirrors how you care for a car. Fuel quality, clean air, coolant flow, and a solid electrical system keep the engine smooth. Here, the “engine” is your burner and heat exchanger. When Error 11 and 12 pop up, they are not random. They point to one of those four basics needing attention.
Act on the simple checks first. Respect the limits of DIY when gas and sealed combustion are involved. Keep records. A technician who sees notes about previous dynamic gas pressure, dates of flushing, and any vent changes will get you back to steady charlotte water heater repair hot water faster.
For homeowners in this region, the combination of gas supply nuances, pollen, and moderate hardness makes preventive care worth the modest effort. Whether you are scheduling routine service, weighing repair against water heater replacement, or planning a fresh water heater installation, build from the fundamentals. Error codes 11 and 12 will stay rare, showers will stay hot, and your tankless will quietly do its job for years.
Rocket Plumbing
Address: 1515 Mockingbird Ln suite 400-C1, Charlotte, NC 28209
Phone: (704) 600-8679