Water Heater Ignition Failure

The unit called for heat, tried to ignite, and failed — you may hear repeated clicking or a brief spark attempt followed by silence. This is one of the most common water heater faults across every brand, and it's usually a gas-supply or ignition-hardware problem rather than anything more serious.

Most likely causes, ranked

• Gas shut off somewhere in the supply chain. The valve at the unit, the valve at the meter, or (on propane) a closed or empty tank — checked before anything else because it's the most common cause and the easiest to rule out.
• Inadequate or fluctuating gas pressure. Wrong gas type after a conversion, an undersized line, meter, or regulator, or a demand spike from another gas appliance running at the same time.
• Air trapped in the gas line. Common right after a new install, a tank swap, or any work done on the gas line — several ignition attempts are sometimes needed to bleed it out.
• Failed igniter or damaged igniter wiring. No spark, or a weak spark that can't reliably light the burner.
• Flame rod fault. On units that ignited briefly and then coded out, a fouled or disconnected flame rod can fail to confirm the flame even when one is present, which the control board reads as an ignition failure.
• Incorrect DIP switch or configuration setting on the control board. Especially relevant right after an install or a board replacement.
• No power to the unit. Even gas units need continuous electrical power to run the control board and igniter — a tripped breaker or GFCI shows up as an ignition failure, not a power-loss message.

This exact fault is documented per brand as Rinnai 11, Navien E003, Rheem 11, and AO Smith 111 on tankless models, and as the flash-code lockouts on AO Smith 2 Flashes and related gas tank codes on storage models.

Check this first

1. Confirm the gas valve is fully open at the water heater, and at the meter or propane tank.
2. If on propane, check the tank level — a near-empty tank can drop pressure enough to prevent ignition well before it reads fully empty.
3. Confirm the unit has power — display lit, breaker not tripped, GFCI outlet not tripped.
4. Power-cycle the unit once (off, wait, back on) and retry.
5. On a newly installed unit or after gas line work, try two or three ignition attempts to let trapped air clear.
6. Note the exact error code or flash pattern shown, if any, before resetting.

Which fault code are you seeing?

If a code or blink pattern is showing, look it up directly: code lookup, or jump to a brand: Rinnai, Navien, Rheem, AO Smith.