What to check, in order
- Don't try to repair it yourself
Vaillant's user manual says fault codes like this are for a competent person.
- Call a Gas Safe registered engineer
Or Vaillant on 0344 736 0049. Have the boiler's model and the code ready.
When to call a Gas Safe engineer
Vaillant's installation manuals give defective electronics as the cause.
A repair visit will usually check the wiring first, then the boiler's control board.
- Note the model and serial number. They're on a label on the data badge, usually under the boiler or behind the front cover.
- Write down the exact code, and what the appliance was doing when it appeared.
- Check whether it's still under warranty. If it is, the repair may cost you nothing.
Quick answers
What does the Vaillant F63 fault code mean?
The boiler's control board has found a fault in its memory, so the boiler won't run.
Can I fix Vaillant F63 myself?
Engineer only (engineer visit). Start with: don't try to repair it yourself; call a Gas Safe registered engineer. Vaillant's installation manuals give defective electronics as the cause.
Is Vaillant F63 worth repairing?
Get a quote first. It points to the circuit board. Ask for a price before agreeing to a new one, especially 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)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.