Read the code before you reset
Every manufacturer uses its own numbering, so the same number can mean different things on two brands. The owner's manual or the manufacturer's website has the list for your model. Write the code down exactly, along with what the hot water was doing and whether other gas appliances were running at the time.
Resetting a unit by switching it off and on can clear a one-time glitch. It can also hide a pattern a plumber needs to see. If the same code returns, stop resetting and get the unit checked.
Common code families
| Code family | What it often points to | Owner-safe checks |
|---|---|---|
| Ignition or flame failure | Gas supply, gas valve closed, low pressure, dirty burner or igniter problem | Confirm the gas valve to the unit is open and other gas appliances work |
| Overheat or high temperature | Scale in the heat exchanger, restricted flow, sensor issue | Note when it happens; check whether the unit is overdue for flushing |
| Low flow or flow sensor | Clogged inlet filter, partially closed valve, debris | Confirm service valves are fully open |
| Venting or air supply | Blocked vent or intake, fan problem | Look outside for an obvious obstruction; do not run the unit if exhaust is smelled |
| Maintenance reminder | Scheduled flush or service is due | Plan a flush per the manual |
Reset, check or call
- IfThe code appeared once after a power blip and has not returnedThenNote it and keep an eye on the unit.
- IfAn ignition code appears and the gas valve was closedThenOpen the valve, then follow the manual's restart steps.
- IfAn overheat or scale code keeps returningThenStop resetting and schedule a flush and inspection with a licensed plumber.
- IfA venting code appears or you smell exhaustThenTurn the unit off and have it inspected before using it again.
Information to give the plumber
- Brand, model number and approximate install date
- The exact code and how often it has appeared
- What the hot water was doing when it appeared
- When the unit was last flushed, if ever
- Any recent plumbing, gas or electrical work in the house
Quick facts
- Codes are
- Brand-specific
- Best source
- The owner's manual for your model
- Repeat codes
- Stop resetting and call a licensed plumber
- Hard-water link
- Overheat and flow codes often trace back to scale
Common questions
Is it safe to reset my tankless unit?
A single reset after a one-time code is usually fine if there is no gas smell. Repeated codes mean something needs attention.
Can a plumber read codes from another brand?
Many can look up any brand's code list, but repairs may need parts or training for that brand. Ask before the visit.
Why did a code appear right after a flush?
Air in the lines, a valve left partly closed or a loose filter cap are common causes. Check the manual's restart steps.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.