Symptoms
- Unit powers on and fan runs but no flame ignites
- Clicking or sparking sound with no burner light
- Hot water never arrives even after running the tap for a while
- May shut down and display an ignition-related error
Likely causes
- CommonGas shutoff valve not fully openA partially closed valve can allow the unit to power on but not get enough gas to ignite.
- CommonFailed igniterThe electronic igniter can wear out over years of cycling on and off.
- PossibleInsufficient gas pressure or an undersized gas lineTankless units demand much more gas flow than tank-style heaters and can struggle on marginal supply lines.
- PossibleFlame sensor fault preventing the control board from confirming ignitionA dirty or failed flame sensor can shut the burner down even if it briefly lights.
What to do
- Confirm the gas shutoff valve to the unit is fully open.
- Check that a demand for hot water is actually being registered, since some units need a minimum flow rate to trigger ignition.
- Listen closely for clicking or sparking at the burner when a hot tap is opened.
- Note any error code displayed and look it up for your specific brand and model.
- Avoid repeatedly cycling the unit on and off trying to force ignition, since gas can accumulate if it's not lighting properly.
- If gas is confirmed on and flow is adequate but it still won't ignite, treat it as an igniter or control board issue.
Tools and parts
- Manufacturer's manual
When to call a pro
Tankless ignition, gas supply, and flame sensor issues are best handled by a licensed plumber or gas technician familiar with your specific unit.
Safety
Use caution
If you ever smell gas or suspect gas is flowing without ignition, stop, ventilate, leave the area, and call your gas utility or a professional rather than repeatedly attempting to reset it.