Water Heater Error Codes: What the Blinking Lights Mean and How to Read Them
Modern water heaters (especially tankless and smart models) display error codes via LED lights or digital screens. These codes pinpoint the exact problem, whether it’s a sensor failure, a gas ignition issue, or a temperature error. Learning to read error codes saves you money by helping you explain the issue to a plumber and avoiding unnecessary diagnostics.
How to Read Error Codes
LED blinking patterns:
Most units use rapid or slow blinks in sequences. For example:
2 fast blinks, pause, 1 slow blink = code “2-1” or “21”
Digital displays:
Show the code directly (e.g., “Error 12” or “F02”)
Color-coded lights:
Red (error)
Yellow (warning)
Green (normal)
Check your manual. Every brand/model has a different code system.
Common Error Codes by Brand
Rinnai (Most Common)
CodeMeaningAction11Flame failureCheck gas supply, igniter12High temp limitLower thermostat, check relief valve14Gas valve errorGas supply/pressure issue; call plumber16Water flow sensor errorLow water pressure or sensor failure20Ignition failureNo spark; check electrical connection
Navien
CodeMeaningActionE001Ignition failureCheck gas and igniterE002OverheatLower temperature settingE003Thermal fuseHeat exchanger issue; call proE004Water flow errorCheck for blockage
Rheem
CodeMeaningAction01Ignition failureGas/igniter issue02High limitTemperature too high03Flame sensorSensor misalignment/failure04Gas valveGas supply failure
General Categories
Ignition codes (1X, 20):
Burner won’t light. Check gas is on, igniter has spark.
Temperature codes (12, 02):
Overheating. Lower thermostat setting, verify relief valve works.
Water flow codes (16, 04):
Insufficient water pressure. Check the inlet filter, descale if needed.
Sensor codes (flame sensor, temp sensor):
Component failure. Usually requires professional replacement.
DIY Troubleshooting Steps
Before calling a plumber:
Check the manual for your model’s code meanings
Verify gas is on (if gas unit)
Check water supply is on and pressure adequate
Restart the unit (turn off 30 seconds, turn back on)
If error persists, note the code and call a plumber.
When DIY Won’t Help
Call a plumber immediately if:
Ignition codes persist after a restart
Flame sensor codes (requires sensor replacement)
Overheat/high-limit codes with an unresponsive thermostat
Any gas smell
Prevention
Keep error codes rare by:
Annual maintenance/descaling (prevents flow/temp codes)
Maintaining water pressure (prevents sensor errors)
Checking the gas supply regularly
Find Local Help
If you’re getting error codes and basic troubleshooting doesn’t help, a plumber can read the code and diagnose quickly.
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FAQ
Can I ignore an error code if the heater still produces hot water? No. Codes indicate problems that will worsen. Address them within days.
Does restarting always clear error codes? Sometimes. If the error returns, it’s a real problem, not a glitch.
Where do I find the manual for my heater? Manufacturer websites have PDFs. Search “[Brand] [Model] manual.”
Sources and Update Policy
This article reflects error codes for 2026 water heater models and common troubleshooting practices.