Tankless Water Heater Error Codes
Updated February 25, 2026
Your tankless water heater displays an error code and stops heating -- common codes for Rinnai, Navien, Noritz, and Rheem with causes and fixes. This is typically a diy or pro fix. Estimated cost: $0 - $50 DIY; $150 - $500 for professional repair.
Overview
Tankless water heaters diagnose themselves. When something goes wrong, the unit displays an error code on the front panel and shuts down. Some codes are simple fixes you can handle in 5 minutes -- like a dirty inlet filter or a venting blockage. Others indicate component failures that need a technician. Knowing what the code means before calling a plumber saves you the $150 service call for a problem you can fix with a screwdriver and 10 minutes.
Symptoms
- Error code displayed on the unit's front panel or remote control
- Unit shuts down mid-use -- hot water goes cold suddenly
- Unit will not ignite at all when a hot water faucet is opened
- LED blinks a specific pattern instead of showing a steady light
- Unit makes clicking sounds (trying to ignite) but no flame establishes
Common Causes
- Ignition failure -- gas supply issue, dirty flame rod, or venting blockage preventing combustion
- Scale buildup in the heat exchanger reducing flow rate below the minimum activation threshold
- Exhaust or intake vent blockage -- birds, leaves, ice, or a disconnected vent pipe
- Flame rod or igniter failure -- components that wear out after 5-10 years
- Low water flow -- clogged inlet filter, partially closed valve, or low municipal pressure
What You'll Need
How to Fix It
- Read and Record the Error Code
Write down the exact code displayed. Codes vary by manufacturer: Rinnai uses two-digit numbers (11, 12, 14, etc.), Navien uses two-digit codes (E003, E012, E016), Noritz uses two-digit numbers, and Rheem uses alphanumeric codes. Check the owner's manual or the sticker on the unit's front panel -- most units have a quick reference chart right there. If you do not have the manual, search '[brand] [model] error code [number]' online.
- Try a Reset First
Many error codes clear with a simple reset. Turn the unit off using the power button or the dedicated breaker. Wait 30 seconds. Turn it back on. Open a hot water faucet and see if the unit fires. Intermittent codes caused by a momentary gas pressure fluctuation, a brief power glitch, or a wind gust at the vent often clear on reset. If the code comes back immediately, it is a persistent problem that needs diagnosis.
- Check Common DIY Fixes by Code Type
Ignition failure codes (Rinnai 11, Navien E003, Noritz 11): Check gas supply -- is the gas valve open? Is there a gas outage? Check the vent -- look for blockages at the exterior termination. Check the inlet filter (small screen on the cold water inlet) for debris. Flow error codes (Rinnai 11, Navien E012): Descale the unit if it has been 12+ months. Check that all shut-off valves are fully open. Clean the inlet filter. Exhaust/venting codes (Rinnai 12, Navien E110): Inspect the vent pipes for disconnections, blockages, or condensate pooling in horizontal runs.
- Know When to Call a Tech
Some codes indicate internal component failures that require parts and expertise. Flame rod failure: the rod that detects the burner flame is corroded or cracked -- $50-$100 part, requires disassembly. Gas valve failure: the electronic gas valve is not opening properly -- $200-$400 part. Control board failure: the main circuit board has failed -- $200-$500 part. Heat exchanger leak: internal crack in the heat exchanger -- $500-$1,000+ or unit replacement. These repairs require manufacturer-specific parts and training.
When to Call a Pro
Call a certified technician for any code that returns after a reset and basic checks, for codes related to the gas valve, flame rod, control board, or heat exchanger, or if you smell gas near the unit. Most manufacturers require warranty service to be performed by authorized technicians.
Prevention Tips
- Descale annually (every 6 months with hard water). Scale is the number one cause of flow errors and overheating codes.
- Clean the inlet filter every 6 months. A clogged filter restricts flow and triggers low-flow shutdowns.
- Check the exterior vent termination seasonally. Birds, insects, and ice block vents more often than most people realize.
- Install a surge protector on the unit's electrical supply. Power surges damage control boards -- the most expensive component to replace.
Frequently Asked Questions
What are the signs of a tankless water heater error codes?
Error code displayed on the unit's front panel or remote control Unit shuts down mid-use -- hot water goes cold suddenly Unit will not ignite at all when a hot water faucet is opened LED blinks a specific pattern instead of showing a steady light Unit makes clicking sounds (trying to ignite) but no flame establishes
What causes a tankless water heater error codes?
Ignition failure -- gas supply issue, dirty flame rod, or venting blockage preventing combustion Scale buildup in the heat exchanger reducing flow rate below the minimum activation threshold Exhaust or intake vent blockage -- birds, leaves, ice, or a disconnected vent pipe Flame rod or igniter failure -- components that wear out after 5-10 years Low water flow -- clogged inlet filter, partially closed valve, or low municipal pressure
When should I call a plumber for a tankless water heater error codes?
Call a certified technician for any code that returns after a reset and basic checks, for codes related to the gas valve, flame rod, control board, or heat exchanger, or if you smell gas near the unit. Most manufacturers require warranty service to be performed by authorized technicians.
How do I prevent a tankless water heater error codes?
Descale annually (every 6 months with hard water). Scale is the number one cause of flow errors and overheating codes. Clean the inlet filter every 6 months. A clogged filter restricts flow and triggers low-flow shutdowns. Check the exterior vent termination seasonally. Birds, insects, and ice block vents more often than most people realize. Install a surge protector on the unit's electrical supply. Power surges damage control boards -- the most expensive component to replace.
When should I call a plumber for tankless water heater error codes?
Call a certified technician for any code that returns after a reset and basic checks, for codes related to the gas valve, flame rod, control board, or heat exchanger, or if you smell gas near the unit. Most manufacturers require warranty service to be performed by authorized technicians.
Can I fix tankless water heater error codes myself?
This problem is rated "DIY or pro". Most homeowners can handle this with basic tools and patience.
How serious is tankless water heater error codes?
This is a medium-severity issue. Fix it soon to prevent it from getting worse.
How much does it cost to fix tankless water heater error codes?
The estimated repair cost is $0 - $50 DIY; $150 - $500 for professional repair. Costs vary by location, severity, and whether you hire a professional.
How can I prevent tankless water heater error codes?
Key prevention tips: Descale annually (every 6 months with hard water). Scale is the number one cause of flow errors and overheating codes.. Clean the inlet filter every 6 months. A clogged filter restricts flow and triggers low-flow shutdowns.. Check the exterior vent termination seasonally. Birds, insects, and ice block vents more often than most people realize..