How to Fix Vaillant F28 Fault Code (UK)
Vaillant showing F28 — Ignition failure. UK diagnosis, likely spare (spark electrode 0020039057) and step-by-step reset.
What the code means
F28 on a Vaillant indicates ignition failure. The boiler locks out to protect the heat exchanger and, on gas faults, to comply with the Gas Safety (Installation and Use) Regulations. Always reset to confirm the code is live, not historical.
Likely spare
The most common fix is the spark electrode 0020039057. Check the exploded diagram against the GC number on the data plate before ordering — Vaillant revised parts on Vaillant units mid-production.
Fix procedure
Gas supply on? Check electrode gap 4.5mm, replace if eroded.
Log the fault and reset. If the code returns within 24 hours, escalate to full electrical diagnosis with a manometer and multimeter.
Frequently asked questions
- Can I reset F28 myself?
- You can press the reset button up to 3 times. If F28 returns, the boiler needs a Gas Safe engineer — it is illegal to repair gas components without registration.
- Is the part covered under warranty?
- Vaillant standard warranty is 2–10 years depending on model. Registered installations get the full term. Check the sticker inside the case.
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