Without a standing pilot light, a tankless water heater has to reliably strike a flame from scratch every single time hot water is called for.
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Quick answer
The igniter in a tankless water heater lights the burner at the start of every hot water draw, since most modern units do not run a standing pilot flame continuously and instead ignite fresh each time flow is detected. It is either a hot-surface igniter, an electrically heated element that glows hot enough to ignite gas on contact, or a spark igniter that creates an electric arc. Igniters fail from element wear after repeated heat cycles, carbon fouling that insulates a spark igniter, or wiring and connector corrosion, which shows up as delayed ignition, intermittent failure to light, or no ignition at all.
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Most modern tankless water heaters do not keep a small pilot flame burning continuously the way older standing-pilot appliances did. Instead, the unit ignites the burner fresh every time it detects enough water flow to warrant heating, which can mean dozens of ignition cycles a day in an active household. The igniter is the component responsible for actually starting that flame each time.
Two designs are common: a hot-surface igniter, which is an electrically heated element, often a ceramic-coated resistive element, that glows hot enough to ignite gas on contact once energized, and a spark igniter, which creates a high-voltage electric arc across a small gap to ignite the gas, similar in principle to a spark plug. Either way, the flow sensor triggers the sequence, the igniter fires, and the flame rod then confirms the resulting flame before the unit continues to run.
Hot-surface igniters are a wear item by nature, since the element is repeatedly heated to very high temperatures and then cools between cycles, and that thermal cycling eventually causes the element material to weaken or crack after enough cycles, similar to how an incandescent light bulb eventually burns out from repeated on-off cycling. Once an element has degraded enough, it either takes longer to reach ignition temperature or fails to glow hot enough at all.
Spark igniters are more prone to carbon or soot fouling at the electrode gap, which can weaken or prevent the arc from jumping reliably, along with general wear at the electrode tip over time. On either type, wiring and connector corrosion at the igniter's base is another possible failure point, particularly in units that have had any moisture intrusion into the burner compartment.
| Symptom | Likely cause |
|---|---|
| Noticeable delay before the burner lights when a tap opens | Igniter is weakening and taking longer to reach ignition |
| Intermittent failure to ignite, sometimes lighting and sometimes not | Marginal igniter performance or fouling on a spark-type igniter |
| Unit fails to ignite at all and shows an ignition-related fault | Igniter element has failed, or fouling is preventing a reliable spark |
| Audible clicking with no ignition on a spark-type unit | Spark is not jumping the gap reliably due to fouling or wear |
Because ignition failure can also stem from a fouled flame rod or a gas supply issue, a technician confirms the igniter itself is the cause through direct testing rather than assuming from symptoms alone.
Diagnosis involves visually inspecting the igniter for physical damage or fouling, testing the electrical resistance or spark performance directly, and confirming gas supply and the flame rod are functioning normally so the igniter is not wrongly blamed for a problem elsewhere in the ignition sequence.
If the igniter shows physical wear, cracking, or cannot reliably reach ignition temperature or produce a consistent spark, it is replaced. Cleaning can sometimes resolve fouling-related issues on a spark igniter, similar to how a flame rod is cleaned before being replaced.
An igniter that is failing intermittently tends to get worse over time rather than better, and a household relying on a tankless unit for all its hot water can be left without any hot water at all if the igniter fails completely. Addressing early signs, like a noticeable ignition delay, before it becomes a full failure is generally the more convenient path.
Any work on the gas line, gas control valve, burner, or venting of a natural gas appliance must be done by a Technical Safety BC licensed gas fitter; CANRO holds gas licence LGA0043870 and boiler licence LBP0046450. If you ever smell gas, hear a hissing sound near the appliance, or notice soot, a burnt smell, or headaches and nausea that ease when you leave the house, leave the home immediately and call FortisBC at 1-800-663-9911 from outside before doing anything else.
Safety note
Any work on the gas line, gas control valve, burner, or venting of a natural gas appliance must be done by a Technical Safety BC licensed gas fitter; CANRO holds gas licence LGA0043870 and boiler licence LBP0046450. If you ever smell gas, hear a hissing sound near the appliance, or notice soot, a burnt smell, or headaches and nausea that ease when you leave the house, leave the home immediately and call FortisBC at 1-800-663-9911 from outside before doing anything else.
No, most modern tankless units do not run a continuous standing pilot; the igniter instead lights the burner fresh at the start of each hot water draw.
A spark-type igniter fouled with carbon can sometimes be cleaned to restore reliable sparking, while a worn hot-surface element generally needs to be replaced outright.
Lifespan depends on usage and cycling frequency, and manufacturers do not publish a guaranteed figure; a technician can assess wear during a service visit.
A gradual ignition delay is a common early sign of a weakening igniter, worth having checked before it progresses to a full ignition failure.
No, this involves the gas and ignition system of the appliance and should be handled by a licensed gas fitter.
No, the igniter is a serviceable, replaceable part on its own and does not indicate a need to replace the entire tankless water heater.
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