How to Replace a Boiler Ignition Electrode (UK)
Swap ignition and flame rectification electrodes on Worcester, Vaillant, Baxi and Ideal boilers. Gap settings.
Worcester BoschVaillantBaxiIdeal
Gap is everything
Ignition electrodes fire across a 3.5–4.5 mm gap. Wear opens the gap — spark weakens — F1 / EA229 lockout. New electrodes ship pre-gapped; don't bend the leg.
OEM part numbers
- Worcester Greenstar — 87161424040 (dual electrode assembly).
- Vaillant ecoTEC — 0020168558 (ignition + rectification set).
- Baxi 800 — 720030601.
- Ideal Logic — 175584.
Fit and gap check
Feeler-gauge the gap before refit. Replace the gasket. Test with the flue gas analyser — flame current must exceed 1.5 µA at min rate.
Frequently asked questions
- Electrodes are cheap — should I fit annually?
- No — most last 5–8 years. Change with heat exchanger or at 8-year service.
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