Tankless water heater showing an error code

Symptoms

• Digital display shows an error code or blinking light pattern
• Hot water may be reduced, intermittent, or absent
• Unit may shut down mid-use
• Error may only appear under certain conditions like high demand

Likely causes

• CommonIgnition failureMany common codes relate to the burner failing to ignite properly.
• CommonInsufficient gas supply or venting restrictionUndersized gas lines or blocked vents commonly trigger error codes on tankless units.
• PossibleFlow sensor or water filter issueA dirty inlet filter or a flow sensor fault can prevent the unit from detecting demand properly.
• PossibleOverheating or freeze protection triggerExtreme conditions can trip safety codes even when the core system is fine.

What to do

1. Write down the exact code or blink pattern shown on the display.
2. Look up that specific code in your model's manual or on the manufacturer's website, since codes vary significantly by brand.
3. Check that the vent termination outside isn't blocked by snow, debris, or a bird's nest.
4. Check the inlet water filter screen, if your model has one, and clean it if it's dirty.
5. Try powering the unit off and back on after checking the above, since a simple reset clears some transient codes.
6. If the code points to a gas supply, venting, or internal component issue, avoid repeated resets and get a professional diagnosis.

Tools and parts

• Manufacturer's manual or model lookup

When to call a pro

If the code persists after basic checks, or it relates to gas supply, ignition, or the heat exchanger, call a licensed plumber or the manufacturer's authorized service line.

Safety