What to check, in order
- Check the pressure gauge
Vaillant's ecoTEC plus manual recommends at least 1 bar and says to top up if it falls below 0.8 bar.
- Top up if it's low
Use the filling loop the way your user manual describes, then check the gauge again.
- Leave air in the system to the engineer
If the boiler or radiators have air in them, Vaillant's user manual says to have your competent person purge the heating installation.
When to call a Gas Safe engineer
If the pressure is fine, call a Gas Safe registered engineer. Vaillant lists a blocked pump or weak pump output, air in the boiler, low system pressure, or a blocked or wrongly fitted non-return valve.
Quick answers
What does the Vaillant F24 fault code mean?
The water in the boiler heated up too quickly, usually because it isn't circulating properly, so the boiler shut down to protect itself.
Can I fix Vaillant F24 myself?
Moderate (about 15 minutes to check the pressure). Start with: check the pressure gauge; top up if it's low; leave air in the system to the engineer. If the pressure is fine, call a Gas Safe registered engineer. Vaillant lists a blocked pump or weak pump output, air in the boiler, low system pressure, or a blocked or wrongly fitted non-return valve.
Is Vaillant F24 worth repairing?
Get a quote first. If it was low pressure, topping up costs nothing. A pump problem is a routine repair, but ask for a price first on an older boiler.
Checked against
- Vaillant ecoTEC plus open vent installation and servicing instructions (PDF)
- Vaillant ecoFIT pure combi installation and maintenance instructions (PDF)
- Vaillant ecoTEC plus operating instructions, 2023 edition (PDF)
- Vaillant ecoTEC plus ..6/5-5 user manual (PDF)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.