How to Fix Vaillant F24 Fault Code (UK)
Vaillant showing F24 — Insufficient water flow. UK diagnosis, likely spare (pump / diverter) and step-by-step reset.
What the code means
F24 on a Vaillant indicates insufficient water flow. 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 pump / diverter. Check the exploded diagram against the GC number on the data plate before ordering — Vaillant revised parts on Vaillant units mid-production.
Fix procedure
Check pump PWM, diverter free.
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 F24 myself?
- You can press the reset button up to 3 times. If F24 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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