Boiler Ignition Electrode: What It Does
The boiler ignition electrode is the small metal probe beside the burner that makes the spark to light the gas; if it is worn, cracked, badly gapped or carboned up, the boiler clicks but fails to light and then locks out.
The boiler ignition electrode is the small metal probe beside the burner that makes the spark to light the gas; if it is worn, cracked, badly gapped or carboned up, the boiler clicks but fails to light and then locks out. The ignition electrode produces the spark that lights the gas at the burner when the boiler calls for heat. When it wears, cracks, or gets out of position, the boiler either fails to light at all or takes several noisy attempts each time.
What it does
A high-voltage spark jumps across the electrode's gap right at the burner, igniting the gas the instant the gas valve opens, within a fraction of a second window.
How it fails
The gap widens or closes with age and heat cycling, the ceramic cracks, or carbon build-up interferes with the spark, all of which delay or prevent ignition.
Repair or replace
Regapping is possible in some cases during a service, but a cracked or badly worn electrode is replaced rather than adjusted.
Ignition electrode or flame sensor?
Many boilers have a separate flame sensing electrode that proves the flame is there once it lights. If the spark is fine but the boiler lights briefly and then shuts off, the sensing side is more likely. If you hear repeated clicking with no flame at all, the ignition side is the first suspect. Both sit inside the sealed combustion chamber, so replacing them is Gas Safe work.
Get delayed or failed ignition checked
Describe the sound and delay when the boiler tries to fire and we'll check the electrode and gap during the visit.
Questions we get asked
Who is legally allowed to replace an ignition electrode?
Yes, this is part of the gas ignition system and is Gas Safe registered work.
Does this affect gas safety if it's delayed lighting?
Delayed ignition can allow a small amount of unburned gas to build before lighting, which is exactly why it should be addressed rather than left.
How often does this need replacing?
There's no set interval; it's assessed and, if needed, addressed at each service rather than replaced on a fixed schedule.
What are the signs of a faulty ignition electrode?
Repeated clicking without lighting, lockouts on start-up and ignition fault codes are the common signs.
Is a boiler ignition electrode checked at a service?
Yes. The electrode's condition and gap are part of an annual service, which is one reason servicing reduces ignition lockouts.