Modern water heaters, especially tankless and digital-controlled models, use fault codes to communicate problems. Think of them as your heater’s way of saying, “Something isn’t right.” Instead of guessing, you get a clear signal about ignition issues, flow problems, overheating, or electrical faults. So knowing a water heater fault code helps you respond quickly. This guide explains the most common fault codes, what they mean, and how to respond, even if with a quick reset or by calling a licensed plumber.
What Is a Water Heater Fault Code?
A fault code is a digital or LED error message built into your water heater’s control board. Similar to a check engine light in your car, it doesn’t fix the problem itself but points you toward the issue.
Manufacturers use fault codes to:
- Speed up diagnostics for technicians.
- Help homeowners recognize simple fixes like restoring power or gas supply.
- Prevent dangerous conditions, such as overheating, ignition failure, or gas leaks.
Codes appear differently depending on the model. A tankless water heater may flash “E11” for ignition failure, while an electric tank heater may display “E5” for thermostat malfunction.
In older models, fault codes might be shown as LED blinking sequences instead of digital displays.
Common Water Heater Fault Codes and What They Mean
Ignition Failure (E11 – Gas Models)
Ignition failure means the burner didn’t light after several attempts. Causes include a closed gas valve, low gas pressure, air in the gas line, or a faulty igniter. This is one of the most common tankless water heater errors.
Flame Sensor Error (E12 – Gas Models)
When the burner lights but the flame sensor doesn’t detect it, the heater shuts down. A dirty flame sensor, corroded wiring, or a misaligned sensor can trigger this code.
Gas Valve Fault (E13 – Gas Models)
This code points to a problem with the gas control valve or regulator. Faulty wiring, improper gas pressure, or a defective valve assembly may stop the heater from running.
Heating Element Failure (E20 – Electric Models)
In electric water heaters, this means a burned-out element. The tank may still provide lukewarm water if only one element fails, but complete failure results in no hot water.
Thermostat Error (E21 – Electric Models)
When the thermostat or thermistor fails, the control board can’t regulate water temperature. This often requires replacement of the thermostat or temperature sensor.
Power Supply Fault (E22 – Electric Models)
A tripped breaker, blown fuse, or loose wiring causes this fault. It signals the unit isn’t receiving consistent power from the electrical panel.
Flow Sensor Error (E30 – Tankless Models)
Tankless heaters need a minimum 0.5 GPM flow rate to activate. A clogged inlet filter, scale buildup, or faulty flow sensor triggers this code.
Exhaust Blockage (E40 – Tankless Models)
Blocked exhaust vents or intake pipes restrict airflow, causing dangerous backdrafts. Codes in the E40 range typically point to ventilation problems.
Overheating Code (E90 – Tankless Models)
This means water temperature is climbing beyond safe levels, usually from a blocked heat exchanger, scale buildup, or a faulty thermostat. Ignoring this code risks overheating damage or safety shutdowns.
What to Do When You See a Fault Code?
Seeing a water heater fault code doesn’t always mean disaster. It’s a built-in diagnostic tool designed to keep your system safe and help you respond quickly. Here’s a clear step-by-step process:
- Locate the Code: Check your water heater’s digital display or LED light sequence. Some models use a two-digit code (like E11 or E90), while older units use flashing light patterns.
- Look It Up in the Manual: Every manufacturer provides a list of fault codes in the user manual or on their website. This will confirm if the issue relates to ignition, flow, overheating, or electrical components.
- Try Simple Fixes First
- Reset the unit with the control panel or reset button.
- Confirm the gas supply valve is open on gas models.
- Check the breaker or fuse for electric water heaters.
- Inspect the inlet filter and clean it if it is clogged.
- Reset the unit with the control panel or reset button.
- Know When to Stop: If the code points to deeper issues like thermistor failure, gas pressure faults, or venting blockages, it’s time to call a plumber. Ignoring or guessing at these problems risks fire, carbon monoxide, or system damage.
Troubleshooting Tips for Homeowners
You can safely try a few homeowner-level checks before calling for professional service:
- Electric Models:
- Check the breaker or fuse in the electrical panel.
- Use the reset button only once; repeated tripping points to a faulty heating element or thermostat.
- Check the breaker or fuse in the electrical panel.
- Gas Models:
- Verify that the gas supply line and gas control valve are fully open.
- Relight the pilot if the model uses one, following the manufacturer’s instructions.
- Verify that the gas supply line and gas control valve are fully open.
- Tankless Models:
- Clean the inlet filter to restore water flow.
- Check the air intake and exhaust vent pipes for obstructions, nests, or debris.
- Confirm that the minimum flow rate (usually 0.5 GPM) is met by opening the tap fully.
- Clean the inlet filter to restore water flow.
Caution: Never attempt wiring checks, gas pressure adjustments, or internal component replacements unless you’re a licensed technician. Always stop troubleshooting if you detect gas odors, visible scorch marks, or water leaks near the unit.
Preventing Future Fault Codes
Preventive care reduces the chance of fault codes appearing and extends the system’s life. A few key practices include:
- Annual inspection: Have a technician test sensors, flush the system, and confirm safe venting.
- Tank flushing: Drain and flush tanks (or tankless heat exchangers) to remove sediment, calcium, and magnesium deposits. Households with hard water should do this more often.
- Replace anode rods (tank models): Prevent corrosion by replacing the anode every 3–5 years. This prevents rust flakes from clogging filters or sensors.
- Install surge protection: Protect the control board and thermostat on electric models from voltage spikes.
- Maintain safe gas pressure: For propane or natural gas units, verify regulators and supply lines annually.
When You Need a Professional?
When water heater fault codes appear, some situations demand professional attention rather than DIY fixes. Ignition failures such as E11 or E12 often indicate a faulty igniter, dirty flame sensor, or low gas pressure, which require specialized tools like a digital gas manometer or multimeter to test correctly.
Overheating errors such as E90 and higher usually suggest a blocked heat exchanger, a failed thermistor, or restricted circulation. Repeated fault codes that persist after resets are also a warning sign of an underlying issue that may involve calibration or failing components.
Licensed plumbers and HVAC professionals carry diagnostic readers, combustion analyzers, and flow meters to confirm whether the root problem lies in the gas supply line, flame sensor, pump, or control board.
Conclusion
Seeing a water heater fault code on your digital display might feel stressful, but it’s your system’s way of protecting itself and warning you that something isn’t right. Some codes, such as power interruptions or low flow errors, can be resolved with simple checks like resetting the breaker, cleaning the inlet filter, or confirming the gas supply valve is open. Others, such as ignition failures, overheating alerts, or control board errors, require a licensed professional to diagnose and repair safely. An awareness of these codes allows you to take the right next step without guessing.
Call ProsWay Plumbing & HVAC for Expert Diagnostics!
Don’t let fault codes leave you without hot water. ProsWay Plumbing & HVAC provides expert diagnostics, repairs, and maintenance for gas, electric, and tankless water heaters across Northern New Jersey. Call us now at (862) 260-5870 or Book Online today for fast fault code troubleshooting and reliable water heater service that keeps your hot water flowing.
